Executable Files

An executable file is a computer file that contains instructions in a form that a computer's operating system or application can understand and follow.  Computers must use executable files to carry out the tasks that you give to them.  Every application you run starts off with an executable program.

What's the worry?

You need to be wary of executable files whose origin is unknown, especially if you receive them through email from an unfamiliar sender address (or even from a familiar one, if you weren't expecting to receive them). 

Generally, to enable these files to perform their function (or, to "open" them), all you have to do is click your mouse button on the attachment one or two times.  Once you run the executable, the computer will perform the instruction set within.

If the file actually contains malicious software, you've potentially unleashed a world of trouble on your computer.

What does an executable file look like?

Every file name has a final part called the "extension."  The extension helps a computer's operating system or application identify what it is, what it does, and sometimes where it should be stored.   You see file extensions on data files so often you may have learned to ignore them, such as".doc" for Microsoft Word files, ".xls" for Microsoft Excel files, and ".ppt" for Microsoft PowerPoint files.

What about executable files -- that is, files that cause actions on your computer?  The most common executable files end in ".EXE" or (".exe"), but, not all end in this extension.  You may also come across executable files that have the following extension:  .VBS, .BAT, .COM, .PIF, .VBE, .DLL and .WSF to name a few.  All represent a potential danger.

These executable files are primarily Microsoft Windows file types.  Other operating systems have different file types for executables but the underlying principle and the way they function is the same.

Are there other ways an executable file can be run or look different?

Yes!  Some files are actually named differently to try to trick you.  For example, what appears to be a picture file of "John Doe" may actually be an executable file named as:  "JohnDoe.jpg.vbs".  You may not see the .VBS extension because it may be hidden.

Executable files may also be run from a Web site.  You may come across an email message containing an Internet URL (Web site address) that automatically runs an executable program when you navigate to that location.  For example, the .COM extension is an executable file extension.  But, if you are familiar with Internet URLs, you will note that .com also represents the designation for a commercial web site like www.cnn.com (also sent as cnn.com) . 

Virus writers have been naming their malicious files with the names of legitimate Web sites.  When you click on what you thought was a legitimate site URL, you might have just run an executable file.

What should I do if I have run an executable file that I didn't intend to or my computer is acting strangely?

If you suspect that an executable file is running on your computer and/or it is behaving strangely, you should turn your computer off and contact our Information Security team.