Moon Secure Antivirus aims to be the best Windows antivirus program based on open source (GPL) code. Like all good antivirus programs, Moon Secure Antivirus offers protection in real time using the ClamAV database. You can specifiy exactly which parts of your network Moon Secure checks even devices connected by USB. However, Moon Secure has very few options although it doesn't consume much of your PC's resources making it a handy lightweight option.