Classification by target:
- Boot sector infector — Infects a master boot record and spreads when the system is booted from the disk containing the virus.
- File infector — Infects files that the operating system or shell considers to be executable.
- Macro virus — Infects files with macro or scripting code that is interpreted by an application.
- Multipartite virus — Infects files in multiple ways.
Classification by concealment strategy:
- Encrypted virus — A portion of the virus creates a random encryption key and encrypts the remainder of the virus.
- Stealth virus — A form of virus explicitly desgined to hide itself from detecion by anti-virus software.
- Polymorphic virus — A virus that mutates itself with every infection.
- Metamorphic virus — A virus that mutates and rewrites itself completely at each iteration, and may change behaviour as well as appearance.
