The function of anti-virus software is to perform one or more of the following functions:

Prevention: Anti-virus programs may be preventive or restorative. Preventive techniques include stopping attempts at direct access such as formatting and deleting, or even write protecting the hard disk while testing familiar software. The restorative process is achieved by maintaining a copy of CMOS information, boot sector information, the file allocation table, etc., in a safe area like a floppy.

Detection

The detectors warm the user of the presence of a virus after it is loaded into the machine or disk. These programs maintain a file with a list of checksum values of the executable files. The identifiers rely on the fact that when the replicates, it makes a copy of itself.

Vaccination: The vaccinators inject some code into the executable files. When the vaccinated file is run, the injected code performs an integrity check on the program being executed and warns if any changes have been made.

Inoculation: The inoculators insert the virus signature into infected areas or files at appropriate location. When the virus performs their self detection, they find their signature and believe that the memory/disk/file is already infected and so do not infect.

Damage control: The better equipped anti-viral programs are also capable of controlling damages caused due to virus attack.