ClamWin is the Windows version of ClamAV, a virus and spyware scanner which database is constantly maintained by a group of volunteers and updates are always available for free. Note that the program does not contain an on-access real-time scanner; you must manually scan a file in order to detect malware or use a third party tool like the general purpose Directory Monitor (see Execute scripts/applications when events occur) or the outdated Clam Sentinel.

ClamWin Portable started out as a portable wrapper for ClamWin, but since ClamWin itself is no longer maintained, ClamWin Portable decided to combine “the latest version of ClamWin from the publisher combined with updated ClamAV Windows native files”, as explained here and here.

Alternatives:

ClamAV is a virus and spyware scanner whose database is constantly maintained by a group of volunteers and updates are always available for free. Note that the program does not contain an on-access real-time scanner; you must manually scan a file in order to detect malware.

ClamWin Portable is a portable wrapper for ClamWin and can be modified to automatically update virus database periodically or during startup.

Alternatives:

ClamAV is a virus and spyware scanner whose database is constantly maintained by a group of volunteers and updates are always available for free. Note that the program does not contain an on-access real-time scanner; you must manually scan a file in order to detect malware.

ClamWin Portable is a portable wrapper for ClamWin and can be modified to automatically update virus database periodically or during startup.

Alternatives: