Avast! FreeAntivirus is a complete anti-virus package, that is is free for registered home non-commercial users.
It contains an on-demand scanner with two interfaces (simple for novices and advanced for experienced users), an on-access scanner with Standard Shield (which protects against execution and opening malware programs) and an embedded e-mail scanner which scans incoming and outgoing email messages. avast!
FreeAntivirus integrates with the Windows Explorer right click menu and also includes a special screen saver which is able to scan your system while your computer is not in use.