Bullguard 7 is an excellent virus scanner, with firewall, anti-spyware and anti spam filter all built in on top of the scanner itself.

The entire package, I bought online for around $60 for a years subscription and as I downloaded it I didnt pay anything for the cd etc...either.

Bullguard can be set to continuely scan your PC in the background, but only to a degree that you don't notice. The virus scanner itself is excellent and much better than any free software out there, I tried at least four different free virus scanner before getting Bullguard and it instantly picked up on viruses all three of the others had missed (including the one giving me hell!).

The anti-spam part also very handily integrates with outlook (and it's worked with other email apps iv used including thunderbird) so it controls the level of spam that you recieve to an excellent degree.

The level of customizability of the package is also awesome, you can make everything manual and set it to ask you what to do each time an infection/attack is found or you can set it fully to auto and tell it what to do in each circumstance so that it never has to bother you. All this and everything in between!

There are also regular updates to the virus definition of the package, I usually get an update each time i start up my PC (daily)