Which of the following append themselves to files as a protection against viruses?

A.
Behavior blockers

B.
Cyclical redundancy checkers (CRCs)

C.
Immunizers

D.
Active monitors

Explanation:
Immunizers defend against viruses by appending sections of themselves to files. They continuously check the
file for changes and report changes as possible viral behavior. Behavior blockers focus on detecting potentially
abnormal behavior, such as writing to the boot sector or the master boot record, or making changes to
executable files. Cyclical redundancy checkers compute a binary number on a known virus-free program that is
then stored in a database file. When that program is subsequently called to be executed, the checkers look for
changes to the files, compare it to the database and report possible infection if changes have occurred. Active
monitors interpret DOS and ROM basic input-output system (BIOS) calls, looking for virus-like actions.