ClamWin is based on the ClamAV open source antivirus engine, which makes ClamWin free and well supported. This antivirus boasts a high detection rate for viruses and spyware and is regularly updated with automatic updates to the virus database.
The virus database is updated several times per day and is made up of thousands of security experts posting findings to the ClamAV mailing list. Note that ClamWin does not offer proactive protection for your PC, but only provides manual scanning of files and email attachments. This makes ClamWin more suited to tech savvy users who understand viruses better and do not want their computer to be bogged down with software that interrupts their computing environment.