The term “retrovirus” has several different unrelated meanings, including:
1. Malicious applications which try to disable, delete or deactivate antivirus systems.
2. A computer virus which attempts to disinfect and repair files damaged by a different computer virus.
3. A computer virus which attempts to run itself by exploiting vulnerabilities in the parser of the antivirus program, file compression program or other program which reads the virus into memory.
Not to be confused with the phase “retro virus” which could mean a modern computer virus that makes use of old techniques to replicate.