How do companion viruses operate?

Companion viruses operate by embedding their code into a targeted program, which allows them to execute when the legitimate program is launched. This method leverages the trust users have in the original application, as the companion virus is typically designed to have a similar name to the legitimate program. As a result, when a user attempts to run the trusted application, the malicious code embedded in the companion file can run instead, potentially leading to the compromise of the system or the installation of additional malware.

The design of companion viruses exploits vulnerabilities in how operating systems handle file execution and can effectively evade detection by users who expect the legitimate program to run without issues. By focusing on embedding their code, these viruses can manipulate the host program's operations, rather than replacing it entirely or residing only in data files. This method makes companion viruses particularly insidious, as they can remain undetected while they execute their malicious tasks.