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F-Secure Computer Virus Info Center

Term Explanations


(MBR, OSboot, COM/EXE, exe, com)

A type of a virus is determined by the different kinds of targets the virus infects.

For example possible targets are *.com files, *.exe files, boot sectors, master boot records.


Some viruses infect both executables, and master boot records. These are called Multipartite viruses.

Overwriting Virus

Overwriting viruses replace the code of the victim with the virus code, thus destroying the victim irreparably.

Companion Virus

Companion type viruses create a same named executable with a .com extension, in order to utilize the feature of DOS which dictates that if there are same named executables in the same directory, the one with the .com extension is executed first.

(NON-) Resident Virus

A resident virus stays in memory after execution. Resident viruses are able to thus spread without the user executing them once they are in memory. Whereas non-resident viruses are able to spread only when the user executes an infected program.

Stealth Virus

A stealth virus hides its presence so the user can not detect the decrease of memory or the increase in infected files sizes.