Your AntiVirus Index provides a measurement of how secure your computer is against the latest virus threats. This index is computed based upon which types of virus threats currently exist and how prepared your computer is to defeat these threats.
One of the factors that influence your AntiVirus Index is external virus threats. For example, if there is a virus outbreak, does your anti-virus software protect you from this virus? Also, other factors include the configuration and settings of your anti-virus software and whether you are receiving ongoing virus signature file updates.