Note that ClamWin is not an active antivirus. The only part of ClamWin active is the tray icon and the signature updater. http://www.clamwin.com/
Please note that ClamWin Free Antivirus does not include an on-access real-time scanner. You need to manually scan a file in order to detect a virus or spyware.
ClamWin comes with the Ask Toolbar. You must watch the install closely and opt out or it will be installed. http://www.clamwin.com/content/view/217/27/
Ask.com shares advertising revenue with ClamWin and our team will use the received money to fund the development of new features.
For further details please see this page http://www.clamwin.com/ask/
That said, I have it installed on my WinXP machine for a second manual scanner.