The Secunia PSI is aFREE security tool designed to detect vulnerable andout-dated programs and plug-ins which expose your PC to attacks. Attacks exploiting vulnerable programs and plug-ins are rarely blocked by traditional anti-virus and are therefore increasingly "popular" among criminals.
The only solution to block these kind of attacks is to apply security updates, commonly referred to as patches. Patches are offered free-of-charge by most software vendors, however, finding all these patches is a tedious and time consuming task. Secunia PSI automates this and alerts you when your programs and plug-ins require updating to stay secure.