Variant: A modified version of a virus that is usually produced on purpose by a virus author or by someone who modifies the original virus. Variants may be very similar to their parent virus, or may be fairly different. Some are text variants, which means that the only differences between them and their parent virus are in internal program comments that are never displayed, or in text that is displayed to the screen. Some are the result of small changes made to the original virus, apparently to create a new virus which is not detected by certain anti-virus programs. Some are the result of large changes, such as combining the spreading part of one virus with the damage part of another.

Virtual Network Perimeter: A network that appears to be a single protected network behind firewalls, which actually encompasses encrypted virtual links over untrusted networks.

Virus: A self-replicating code segment. Viruses may or may not contain attack programs or trapdoors.

Vulnerability: This term refers to any weakness in any system (either hardware or software) that allows intruders to gain unauthorized access or deny service.