An executable file is a computer that has the ability to run a set of commands on your computer. By now, you should know that any app or program that can run on your computer can contain viruses. And these viruses can create havoc on your computer system. Every time you download a file from the Internet, or copy a file to your computer (from a USB drive, CD, etc.), you should be concerned on whether that file is going to infect your computer.

Recently, I came across this web page that lists many of the executable file types. There are probably some that are missing from this list, but it contains many of them.

List of Executable File Extensions

Below is a PARTIAL list of that page, just for example. Notice that MP3, PDF, MOBI, JPG aren’t on the list. These are files that contain data, not an executable script of code. It’s important to realize the difference, though it’s not unfathomable that these files could be used in the future to transfer malicious code, too. Due diligence is required to keep your computers safe.

UPDATE June 29, 2013: A reader pointed out that I mistakenly added PDF to the “safe file” list. Scott writes:

I want to make one correction to your latest email, specifically, where you reference the web site that you came across and discuss that MP3, PDF, MOBI, JPG are not on the list because they contain data and are not executable script code, etc…

This is a complete mistake. PDF files, JPG files, and may others are the current hotbed for attack. The following website is one that is a good example to show others that PDF (and some other) files are a threat and anything that you introduce to your system should be suspect, even when from a trusted source… http://www.malwaretracker.com/pdfthreat.php

Scott’s exactly right. I should have done further research on PDF files specifically, instead of focusing on executable files. If you’re not running malware detection on your computer (and why not?), you can scan your PDFs for viruses here: wepawet.cs.ucsb.edu.

Make sure you click on the above link for the full list (the below is about half of the concerned filetypes listed).