A type of computer virus that compromises a feature of DOS that enables software with the same name, but different extensions, to operate with different priorities. For example you may have program.ex [..]

A virus that creates a new program with the same file name as an existing program, but in a different place or with a different file type, so that typing the program's name on the command line causes the virus program to be executed instead of the original program.

A companion virus is a complicated computer virus which, unlike traditional viruses, does not modify any files. Instead, it creates a copy of the file and places a different extension on it, usually . [..]