What Kinds of Files Can Be Viruses?

▼ 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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[ThioJoe]

Corrections & Notes:
• The JS file is actually JScript, not Javascript

[wakaneut]

Making file extension hidden by default is one of the worst mistakes MS did.

[gFamWeb]

The fact that "Hide File Extensions" is SILL on by default baffles me.

[random_person]

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.

[DerLung]

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)

[Kierownik]

Fun fact, in older versions of Windows the .msp files were used by Microsoft Paint.

[evanbelcher]

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.

[TheAndroidGingerbreadGuy]

He may not be a OneDrive synced file, but never fails to upload 💯

[Freddy_Guy]

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

[markanderson]

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.

[ThatOneRobloxDev]

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.

[MechPaul]

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.

[LuigiMordelAlaume]

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.

[Gauley_]

Thanks for having captions, sometimes i have to watch without audio like if my bluetooth headphones run out of battery, helps alot!

[charleshines]

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.

[avishjha]

Something I was literally wondering about only a couple hours back when downloading an MP3 like the old days. Great timing!

[fightingtable]

ThioJoe I really appreciate you adding subtitles to your videos, they are very useful

[neoqueto]

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.

[nutherefurlong]

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

[faenethlorhalien]

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!