The Secunia Personal Software Inspector (PSI) is a free computer security solution that identifies vulnerabilities in non-Microsoft (third-party) programs on your PC. Vulnerable programs can leave your PC open to attacks.
Simply put, it scans software on your system and identifies programs in need of security updates to safeguard your PC against cybercriminals. It then supplies your computer with the necessary software security updates to keep it safe.
Using a scanner like Secunia PSI 3.0 is complementary to antivirus software, and as a free computer security program, is essential for every home computer.
http://secunia.com/vulnerability_scanning/personal/