Microsoft Security Essentials

[DarkPenguin]

It is free for those that have legit copies of Vista or Windows 7.  Not sure about Windows Xp.

It doesn't have a firewall so use the Windows built in firewall or download a freebie like Comodo or PC Tools.

http://www.microsoft.com/security_essentials/

It is my understanding that it isn't just a re-badged version of, the now discontinued, Microsoft One Care.  That was a wee bit bloated.  This seems pretty lightweight so far.

[Rhossydd]

Works fine on XP sp3

[DarkPenguin]

BTW, it cracked open some spam filtered emails and trashed them as being virus ridden.  These files existed when I had One Care on the machine.  I'd say it has a new detection engine.

Still looking for a lightweight firewall.  I would just like a better interface than the built in firewall has.