What is the 3 parts in a virus?

There are three (four in this case) subroutines common throughout most viruses: the search method, the infection method, the stealth method, and the payload (optional).

The search method enables the virus to determinate infected files from uninfected files and infect the uninfected ones.

The infection method allows the virus to inject its code into uninfected files found by the search subroutine.

The stealth method is what masks the virus's activities not only to the user, but also to the operating system and other security software installed on the host computer. Not all viruses have this subroutine.

The final (and optional) payload subroutine is the section of code in the virus that allows the malware to cause destruction to the infected computer, such as deleting files, stealing confidential information, locking the user out of their system, etc.