Companion virus

Is a type of virus that uses two typical Windows properties:

• Windows does not require file extensions to run a requested file.
• When more than one file qualify for a command, Windows chooses the one that comes first alphabetically.

To illustrate, let’s say you want to run ipconfig from the command prompt. If you do not specify the extension, this normally runs the file ipconfig.exe. However, if there is a file (companion virus) in the same path that is called ipconfig.com, this is executed as, alphabetically, it comes first before ipconfig.exe.