A worm is a program that distributes itself in multiple copies within a system or across a distributed system. A worm attack is a worm that may act beyond normally permitted behavior, perhaps exploiting security vulnerabilities or causing denial of service.
The Department of Defense Technical Rationale Behind CSC-STD-003-85 (U.S. DOD, 1985b). Guidance for applying the TCSEC to specific environments.
Zentralstelle für Sicherheit in der Informationstechnik. The German Information Security Agency (GISA).