This is the Software Publisher's description.
Secunia PSI 3.0 is a free computer security solution that identifies vulnerabilities in non-Microsoft (third-party) programs which can expose PCs to attacks. Simply put, it is scanning software which identifies programs in need of security updates to safeguard the data on your PC against cybercriminals. It then supplies your computer with the necessary software security updates to keep it safe. The Secunia Personal Software Inspector (PSI) even automates the updates for your insecure programs, making it a lot easier for you to maintain a secure PC. 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.