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▼ Time Stamps: ▼
0:00 - Intro
0:54 - File Categories
1:12 - Executables
1:36 - Libraries
2:08 - Scripts
2:37 - Documents Containing Scripts
3:05 - Archives
3:19 - A Good Thing Indeed
4:37 - Specific Files to Watch Out For
4:55 - Executable File Extensions
6:02 - Script File Extensions
6:40 - Very Good Tip
8:01 - Shortcut Files
8:59 - Library File Extensions
9:20 - Archive File Extensions
10:37 - Document Extensions
12:10 - Extra Note About Office Files
13:13 - Final Advice
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Merch ⇨ teespring.com/stores/thiojoe
⇨ / thiojoe
⇨ / thiojoe
⇨ / thiojoetv
My Gear & Equipment ⇨ kit.co/ThioJoe
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Corrections & Notes: • The JS file is actually JScript, not Javascript
Jscript is just JavaScript (ecmascript technically but who's counting)
@@yoyoyononoI am counting 😂
@@random_person6181. 2. 3. 4.
"Run" is the past participle of "run." "Ran" is the simple past of "run." "I have ran" is wrong. The more you know, the less you don't.
WHAT
Making file extension hidden by default is one of the worst mistakes MS did.
This got me the other day at university, was using windows server virtual machines to make a simple web server, couldn't figure out why index.html wasn't working until I remembered stupid hidden file extensions... and it was actually index.html.txt 😫
not in the 90s
To be fair, most people when they would rename a file, they would include the extension and later get upset that Word would be unable to read their Invoice Tax 1996 as there was no association for that Invoice Tax 1996.doc file.
many* not worst
@@Mario583aWindows litterally warns you that you should not rename the file extension. Do people just ignore that pop up???
I want to add a fact in your point that "sometimes hackers may hide the malicious files so that you can't see them by default." Even after you enable the "Show hidden files" option, sometimes they may hide it as a system file (by setting the -h and -s attribute to it). So if you're skeptical about such an item, make sure to enable the "Show hidden operating system files" as well.
Showing OS protected files is kinda risky though
@@cycrothelargeplanet No it isn't risky if you know what you're doing. If that is for destroying a Windows installation, then it's bad otherwise it's not if you want to hunt malware down.
@@random_person618 "it isn't risky if you know what you're doing", I mean... duh!
@@swayingGrass Well I'd like to say this to @cycroplanet.
@@random_person618No, I'm saying that is basically the same as saying "get gud so you're not bad" in a game. It doesn't address the concern, i.e. what is there to know so it won't be dangerous.
The fact that "Hide File Extensions" is SILL on by default baffles me.
STILL* lol
tf is sill
oh ok cool@@gFamWeb
He misspelled "still"@@crosssans9984
Microsoft doesn't care, so takes the easiest, often least secure, path. I retired 15 years ago, so have been able to go MS-free even though I got pretty good at resurrecting MS work stations by then, taking less than a week to bring my machine back from the dead pretty regularly. I could have gotten more than 50% more coding done if it hadn't been for MS trashing itself every few weeks. I got pretty good about doing my thinking and design while waiting for various recovery/restore and re-install programs to do their work. Meanwhile, a 15 year-old Mac with Intel CPUs & GPUs cooked itself and trashed the internal HDD. Once I got the HDD to the point of alive, it took just an hour to restore the backup and have my Mac back up to where it had been before, including passwords on sites I didn't remember wanting to access.
Fun fact, in older versions of Windows the .msp files were used by Microsoft Paint.
I don't believe that!
@@KryzysX It's true
MicroSoft Paint, makes sense
I knew that. Good for me
And .MSA files were used for Microsoft Agent
I absolutely don't understand why file extentions aren't shown by default in windows. It's not annoying and soooo important and also useful (for example if you have two files of different type (like a word document and a pdf export of it) with the same name and have to find the right one by icon)
Yea for real
probably because it looks smoother
For beginners they cant easily disable files by o erwriting file types. Pros usually use different programs than explorer, so they dont card, for the rest you can enable it
@@Lofote do you mean accidentaly overwriting the file extention when renaming a file? That‘s not that much of a problem becauee the extention doesn‘t get highlighted when renaming
well you can select it manually after you press 'rename' and people who just got windows and don't know what file extensions do could just rename the whole thing and remove the extensions@@DerLung
Also worth mentioning, file extensions are just labels, and they can be manipulated at will regardless of the underlying data. So you might run a .cmd file or something, but the rest of the payload may be contained in a file with extension .docx exactly like a normal document, when really it's just a .dll with the extension changed.
True, but Windows won't run it by default in a way that the malicious content comes into effect. If not Windows itself is vulnerable.
Windows uses the file extension to figure out what kind of file a file is, whereas Linux distros use the actual contents. I'm actually not too sure if Windows will allow you to link a non-DLL/LIB file.
You also have ".jar" which is an executable java application. It's basically an executable version of a zip file, where java classes are stored within. Any code that is inside a ".jar" file will be executed and ran when you execute it.
Yea, especially the games which use .jar, .dll files which can be played by the bat file
Java isn't a windows default program tho
Yes, I got some kind of malware trough a jar file. (Minecraft mod) It executet a powershell script which would have downloaded a RAT from github, fortunally that was blocked and the jar file itself „just“ stole my minecraft session token.
Also, docx, xlsx, pptx, etc are actually encoded as zip files. If you change the extension to zip you can see the bundle of files. This can be exploited, unknown office files should be opened in zip explorers before office.
He may not be a OneDrive synced file, but never fails to upload 💯
You can uninstall onedrive but you can’t uninstall thiojoe
@@tfrthats right
Who uses OneDrive? Lmao
@@xXVibrantSnowXxmany
@@tfryou cant install him in the first place :-D
I think the main thing or key from this is don't download things willy-nilly over the internet, use extreme caution with links in email, texting, IM's etc. Always exercise caution with attachments. Only go to reputable trustworthy sources with a careful eye. As much as I like open sources that's where you really have to be careful because of too many hands accessing the source code. But that does not mean that someone can't still attach or inject a malicious code to a paid licensed version either. Buyer/ end user beware! You are your own first line of defense, watch dog and security. Pay attention to everything, because you really have to. All the more reason to have backups should one slip past you, in hopes that you can recover. Thanks for the video Theo.
What's an IM?
Sometimes it does take one slip up. If you ever run a file that closes and doesn't seem to do anything there is a chance that depending on where it came from it may steal passwords and other things and send them to some random person who you most likely never met or knew existed.
Win+R, ipconfig. Omg hacked. 😝
I work in the antimalware industry! More common than changing file extensions or default programs for opening files, we edit local machine group policy to prevent execution on specific file types within a folder that we dedicate to malware. Also, to preserve file names to the extent possible (and to prevent execution and changing default program associations), we just add underscores to file extensions (.exe_, .js_, .scr_). I understand that given the sponsor you wouldn’t show how to edit defender settings, but you could have gone over how to use bitdefender to better protect yourself. Antiviruses have similar settings.
@@Biwiyejowjs tarballs are essentially a zip file without any compression. They're just as safe as any other container (7z, zip, rar)
Conclusion: literally anything can be malware
You know it will be a good day when ThioJoe uploads.
True.
I just love how ThioJoe makes the highest quality tech content on the platform He doesn't resort to clickbait or becoming a Linus clone He has his own style and I literally can't find anyone who makes similar content and at the same level of quality Keep up the good work
@@MasterCraft_48 he's dunking unoriginal people that clone linus' content
@@deathtidegame im stupid nvm...
Yep. Love him. Most people bring up his past videos. Bruh he changed. He is great with the information he provides. Very organised
@@just.nobodyI do miss Joe’s old troll videos though lmao
Bro forgot the windows 9 video 💀💀💀💀💀 edit: nvm that was linus who did thay
Thanks for having captions, sometimes i have to watch without audio like if my bluetooth headphones run out of battery, helps alot!
for example, i can *literally* rename *"executable.exe"* to *_"executable.txt"_* _(or any other file extension)_ and still be able to *run it* under *command prompt* by normal means, the "executable.txt" will be opened in notepad because it has the .txt extension which windows will interpret it as a "text file" (even viewable in the preview pane in explorer)
But then the code that is executed is not insde that file
@@Lofote what do you mean by that?
@@johnpatrickadem6294 the exe is directly loaded into memory for the cpu to execute. So it contains cpu executable instructions, the txt will trigger notepad or a different program to read and parse
hmm, four replies but only three replies, seems legit...
@@LofoteWhat does that mean
Important note: Windows can include meta characters into filenames, for example a right-to-left character. This can lead to characters in filenames being displayed in unusual orders. A common filename this is used in is something like nice-arcs.jpg is acutally a src file, not a jpg
always love and appreciate those proper subtitles!
Something I was literally wondering about only a couple hours back when downloading an MP3 like the old days. Great timing!
You shouldn't ever fully trust any file type really. If your picture viewer has a vulnerability, a hacker can take advantage of it by embedding malicious code to something like a JPEG. Video files, image files, sound files, game data files (it's not too uncommon for cracked games to have functions in them that allow them to load external files from the game directory and those are the real malware). Even text files aren't universally safe because theoretically a text editor (or its part, like a syntax highlighting library) can be susceptible to some kind of code injection.
I got a virus through a pdf loaded in an open source pdf book reader. Ironically a programming textbook
There are also xlsb files that can contain macros. It is the same as xlsm but instead of the XML format it is saved as Microsoft's Binary type.
I wish you had mentioned in the summary at the end that technically at some level ANY file can become an issue if the program that opens it is ubiquitous enough and has a bug. This used to be a big problem although (maybe) DEP solved it back in the xp/vista days when MS had a bug that let a JPG run code (The GDI+ JPEG parsing vulnerability published in September 2004). With the amount of layers that need to fail for it to be an issue I wouldn't worry about it TOO much as long as you keep up to date on your updates. But it is a good reminder to keep up to date on your updates if nothing else.
DEP is a mitigation, not a solution. It makes the task more challenging for the attacker, it doesn't remove the vulnerability.
@@henke37 True. Which is why I feel he should have mentioned it in the video. It's a layer that tries to solve the issue of accidentally running bad code. Like the mark of the web (that he mentions in the video), UAC, windows defender, and remembering to keep up to date on your updates are all layers. But even with all these layers it's (maybe) just one bug away from being an issue.
I was looking for one of these comments (and I’m glad you thought about this too). While the bug you’re referring to may have been patched long ago, there are still bugs just like it that have been recently discovered or have yet to be discovered. Security updates only resolve bugs that have been discovered. Fortunately however (for anyone reading this), you have to *try* to get hit by one of these exploits. They are very rare and are mostly used in targeted campaigns (refer to APTs).
ThioJoe I really appreciate you adding subtitles to your videos, they are very useful
Respect for having good captions and chapters
CMD,ZIP,BAT and EXE are the ones to usually be thought of, no idea it went this deep!
The correct answer to "Which Kinds of Files Can Be Viruses?" (the title of the video at the time of this writing) is actually: "Any file that can be opened." The files listed in this video are merely the ones that can perform malicious actions on their own, i.e. without tricking the program opening them into doing things it's not intended to. I think that's important to keep in mind, because failing to do so may lead to letting one's guard down at the wrong moment.
Some files can even infect your computer without being opened with the right vulnerability. Pretty sure it's been patched but Windows Explorer had a real nasty vulnerability that would allow ACE via rich text documents being thumbnailed.
@@mgord9518 That's correct. Files don't necessarily have to be explicitly opened by the user. Some applications may automatically open a file without user intervention (e.g. by Windows Explorer for the purpose of generating thumbnail as you mentioned). I hadn't really thought of that, but you're right: that's also opening the file and therefore a potential attack surface.
literally every comment is "can we give a moment to appreciate how much work thiojoe puts into his videos"
becuase they are all true!
One type of annoying virus that I got back in 2001 was )and it was called redbot or redcode or redsomething, it got very spread back then...) that the file would arrive to you as a DOUBLE extension file, but Windows (2000 or xp or 98 or me or whatever you used) would only show you the LAST one, hiding the second to last extension which was the actual extension. So, the OS would show you it was a JPG, for instance, and mark it with the icon of a picture, but when you tried to open it, it was actually a VB script and it WOULD ATTEMPT TO RUN IT as a VB script, instead of failing to open it as a JPG, and then you were fucked. That virus would scour through your Outlook contact and sent mail list and send itself to everyone. I had to send SO MANY apology mails to people because of it!
Are you referring to CodeRed?
Thanks for this. Might be good to revisit PDFs some day since the landscape seems to have changed. Like a lot of people read in-browser now, with stuff like Firefox's built in browser that I guess approaches reading differently, but I don't feel like there's strong confidence in what are the preferred routes for using those files
This is the video we didn't know we need but needed.
Thanks for the excellent video TJ ! Very well done as always. Clear, concise and to the point. Please keep up the amazing work. For I appreciate your content. !! 👍👍 ⭐️⭐️⭐️⭐️⭐️
I’m surprised you didn’t mention .jar files. I’ve heard they have been used a ton by hackers/viruses and every time I download one my pc tells me it could be dangerous and I have to manually tell it to keep the file every time.
.jar files are .zip files in disguise, optionally with some metadata (as a file in the archive itself) for the Java Virtual Machine.
@@underrated6902 The only reason I really know about them is because they are used for Minecraft mods. Other than that I haven’t really seen them used.
In fact, these things like jar files, but also msi files and certain kinds of cab files are all just archive types with a file association, which makes them exacutable. Note that jar files do not work on every system, because Java needs to be installed for them, which is not the default, and even msi and cab need Windows Installer to be there, but which is normally the case. All these are normal archive types and don't have a PE header like exe or dll and are never executable by themselves. Self executing archives do also exist however, which contain a full PE application binary followed by the actual archive behind it as a payload. The application simply has the task of unpacking the actual archive, which may be in the form of an installer like approach, but it can also be an application that automatically unpacks the archive into a temporary location and starts another application that was packed inside the archive.
@@underrated6902 ???? no they aren't. They are self containing (except for the JVM) java programs. They are nothing alike zip files, which is an archive format that uses compression
@@mega_gamer93 Yes they are. Jar files are just ZIP archives, with compiled class files inside it and a META-INF directory containing a MANIFEST.MF text file with extra information. Very simple. The trick is that the Windows registry has a java -jar command pre associated with the jar file extension. A thing created by the installer of the Java runtime environment.
You did not mention HTA files, which are HTML applications. Although if I am right these don't work on modern Windows versions anymore, but on a bit older versions they worked and they are are basically just like VBS and JS files, because they have unrestricted system acces via VBScript or JScript, but then embeded in an HTML code and opening with a real window a bit like Electron applications do today, but then using Internet Explorer as their engine instead, since we are talking about a really old technology.
HTML files or .txt ... I mean txt files can be executable...
I didn't know all of these, good video!
Thank you. I was just thinking about this very question earlier this week.
Thank you for being a stable voice in this wilderness.
Thanks Joe I did not know of all of these file extensions.
DLLs can be a lot more dangerous than may be immediately obvious, you don't even need to directly do anything for there to be a problem. A malicious dll file in your download directory might be inadvertently used by some exe in your downloads that you run later, this is very dangerous if the exe is an installer running elevated calls into a malicious dll by accident. This is one reason why auto download exploits are a problem as the malicious file might cause trouble later even if it doesn't immediately cause a problem. You should never leave untrusted dlls in locations where programs might be run from. This can also be a problem with the temp directory so it is a good idea to clean out your temp directory regularly. Dlls in temp can be a general problem even if not malicious as poorly coded installers might leave dlls in the temp dir that interfere with other installers that also want to run from the temp directory. The Installers and dlls in temp problem is mostly an issue with older installers. More modern ones are coded better to try and avoid the temp dll problem. Microsoft over time has attempted to mitigate dll attacks but the solutions are not perfect.
This guy always has good videos for years now
Good video. Thank you for protecting us, soldier!
this is gonna filled with information thank you so much
I love how his recent videos are all genuine and not satire like his old videos back in 2015-2017
I already known all these but i wasn't sure. Thanks ❤
Informative and to the point
You should just assume ANY kind of file can be an exploit. Remember image formats can exploit weaknesses in the rendering programs. Etc
Any file can be a virus if opened by a program with an exploit
Thankfully most exploits are tightly kept secrets.
I do not think the Chinese goverment will use their malware to infect a random person on the internet
For archived files, its pretty much unlimited. you are able to make a compressed folder and rename the 'zip' to just about anything, you just need a tool like 7zip, or winrar to open it.
That's great, sobriety can be something really difficult especially if you have a previous addiction. Stay safe
Congrats on 3 mil!
Translate: Congratulations on 3 thousand! 🤦
@@koopatroopa6882 hes at 3 mil subs lmfao
nice drop bro, appreciate the warnings :) this stuff is really important. Your video helped me explain how to keep my parents safe and your videos helped us a lot in general really
Just get Linux and don't worry about any of this.
my parents have used windows 8, 10 and 11 and i dont have the heart to force them to switch (also would get my ass whupped for trying)@@centuribejewelian
@@centuribejewelianyeah a nice idea to let old people/parents that don't know a lot about computers use linux....😂
It may be that Linux may be safer. Or it could be that the user base pf Linux are safer
Thanks for a thorough review. I wonder, if one has common sense, does one needs to run an antivirus software at all? I mean, there are huge privacy concerns - an antivirus runs all the time, has access to all of your files. Who knows what it’s doing with all that information…
Thanks proper subtitles
Nice video, I would however have added one extra thing to talk about the shortcuts. Inside a shortcut you aren't just limited to running other files, but you could make the shortcut point to something like 'C:\Program Files (x86)\[some web browser like IE]\*.exe [some website]/virus.bat' and then even without that file being on your system, that shortcut will download the file using Internet Explorer. With some extra editing via Notepad I think you might also be able to include the bad code right in the file without the use of other files or programs. Stay safe lol. Great video Thio
Education is the best preventative, Thank you for sharing and informing.
Thank you for all your content, as it is unassailable and very valued. So I pose the question: are use system, mechanic, ultimate for both virus, malware, system maintenance combination, suit. I know Bit Defender is a superior program for defense and monitoring, can you recommend a program for system maintenance that can be integrated into Bit Defender?
I asked this on reddit, thanks for video
I would add a 6th and a 7th category. If an attacker knows that you use some outdated piece if software (including OS components) with a security hole allowing an attacker to execute any code it can be used to deliver malware. It can be a targeted attack specific to you, or can target everyone who is a registered user on a web page (forum, etc) about the outdated piece of software. I have also seen malicious code in source code form. Targeting people who would copy lots of code from questionable sources to their own solutions.
this is really good to know Thanks!!!!!!! :D
I remember when I learned that changing the file extension has nothing to do with what the file is, and you can freely change it back without ruining it. It was like The Matrix
Great information, thanks!
12:55 the zip file itself can't store the "mark of the web", but if the zip file has that mark, all extracted files will inherit it if you use Windows' built in extractor. 7Zip among others doesn't mark the extracted files, so you should still be careful. The mark of the web is actually an alternate data stream on the file called "Zone.Identifier". It's text data and you can even open it in notepad. The easiest is to use the command prompt. Notepad my-downloaded-file.zip:Zone.Identifier
The more you know
PROPER SUBTITLES nice
You're an Angel. Thank you.
Hey Joe, have you done a video on the 'Hosts' file in many operating systems and some devices? It's quite handy and a lot of sites publish custom Hosts files to block online content and ads. A free alternative to spending money on ad blocking software.
Hosts file can be edited as admin and retains those changes and will not revert unless prompted. It is a root level DNS resolver pathway, not only on WinOS, but on MacOS and AndroidOS amongst many others. The only platform that locks out the user is iOS.
ThioJoe always dropping videos on my shower thoughts
This guy used to trick me into taping batteries on my ethernet cable, now hes helping everybody out
Fun fact. I had set the poweshell limitation i saw in his poweshell video and it breaks visual studio installer. It gives a completely arbitrary error, so if you are failing to install or upgrade visual studio after applying poweshell security settings, remove themand retry. It is to bad as it is easy to do a simple bat file that can temporarily clear and reset (run as admin) which means ms could have done the same since vs installer also requires admin.
I remember a great Win XP SP0 exploit where just hovering the mouse over an MP3 file could get you infected due to malformed ID3 tags and the mouse tip. Good times.
it was very helpful, thank you
Our lecturer showed us just how nuts a simple word macro is. Full remote access with some social engineering, and made stronger via obfuscation. Crazy.
This guy’s merch is top notch
Don't open a random powershell script
dont open a random file*
Thanks Joe!
The file extension is also in "view" just on the windows file explorer
Windows' built in zip archive extraction code should probably add that "mark of the web" to files that are extracted from a zip file which also has that mark of the web.
Do a video explaining the origins of file extension types. Like how they chose or came up with executable, png, jpeg batch, etc etc.
All file extensions are abbreviations of words. PNG stands for Portable Network Graphics. JPEG is Joint Photographic Experts Group.
@@simontay4851 interesting!
Thanks for these warnings! Did Windows patched the ability to have the actual extension _before_ the dot?
Literally what everyone using a computer should know!! I didn’t even know some of these!!!
Today I learned why ps1 game isos don't use ".ps1" as an extension.
lol
pls make video on long-term personal data storage tips like mdisc etc...
The laroux virus in the late 1990s was a macro that copied itself into a hidden excel sheet of all your open excel files. I wish there was an easy way to delete a macro from one of these files.
The savior of our laptops(or desktops).
batch files and vbs files are not an issue, there is a modify option when you right-click it
I downloaded Polybridge 2 from some Russian Site. It was an .iso file. I mounted and ran the .exe file. Everything worked great 👍
Bro's flirting with disaster 😭
@@k8rgrl nah PC still working 👍
@@ImDuck42 That's what people stealing your data want.
@@ImDuck42 homeboy really found the one guy that actually had candy in his van
And then there is the most insidious file, a file that is not supposed to be executable , but is contains deliberately malformed data which is designed to exploit the software reading the file to cause it to buffer overflow or fail in other ways and then execute data as code. Pretty rare. but IIRC this has happened with a certain image format in order to exploit an internet browser in the past.
In certain situations (e.g. software with buffer overflows, script injection volnurabilities, bugs causing denial of service, not checking input file size), ANY file (image, audio, video, ...) opened in such a program can be dangerous (although of course it's less common).
Goated ❤❤❤❤
One file type that I can definetly say is secure (because I am the one who wrote the file type specification) is .l2db (Lampe2020-DataBase), which is a simple, binary database. You can of course store malicious code in it (the same as you can in .zip files), but it is really non-trivial to execute that. And the format doesn't support encryption, so you cannot smuggle malicious stuff past a good antivirus inside one of those.
No file type is safe, it completely depends on implementation. If someone were to make a bad parser for your format, it could potentially lead to code execution. Of course this is primarily an issue with much more complicated file formats that probably have some feature regarding macros/scripting but anything is possible when buggy software is involved.
@@mgord9518 If the parser is safe the file is safe, but theoretically you could of course also make an SQL database file dangerous with the "right" vulnerabilities in the parser.
thanks for putting timestamps (i skipped the sponsor)
hey quick question have you ever heard of .nodes? i just remember that while some discord server was being raided one of the raiders sent a .nodes file with obvious virus name. i never saw .nodes so i wanted to see what it is but found nothing only .node and no i dont have the file since i was not familiar with that file and decided to not get it on some pendrive
Best tip out there: just assume that all files could have a chance of having viruses. It's that simple.
Yes, VBS 😅 ive created some loops myself and got scared of my own virus
why. just why
I made a bat forkbomb and waited too long to kill it and froze my laptop
lol 😅@@XnoobSpeakable
i made a program that repeatedly rickrolls you
because its funny (it wasnt public i just made it for myself)@@crosssans9984
What widget/s are you using to monitor system resources on your desktop?
I had a small scare recently. Was browsing a site that constantly gave me pop up ads and one of them auto downloaded a file. Needless to say, i deleted that as quickly as i could and im not planning to return to that site ever again lol
How do you view scripts that are embedded into .PDF documents? I occasionally get .PDFs in emails and then a popup from Norton saying that it stripped out a script from the document
.xlsb-files in Excel also support macros!
Okay, you are extremely amazing because I not only didn’t know what type of files these were, and am always grateful for knowledge, but also I thought .zip files were safe Apparently not all that safe lol, I’ll only be opening those if they’re from trusted sources, like my mom after double checking she sent that.
THIS GUY IS REALLY EXELLENT