Windows 7 antivirus

Avira
http://www.avira.com/en/downloads/
It's light on resources, has live updates, real time protection, and is free.

Avast has good heuristics and is an overall (to me) superior scanner to vira. Avg is good too. All are free.

You can get them all (and other good free apps) from http://www.filehippo.com .

There's also Panda (cloud computing version) that is pretty good too.

Avast I like best.

Avast is good. I'd stay away from AVG. AVG is heavier on the resources and doesn't catch as much.

aford is right about AVG being a pig on resources. If you dont have a newer computer (Core 2 Duo at least) stay away from AVG.

Download & Install the following 3 freewares. It forms a free complete security suite for your system!
1. Avira Anvivir - http://www.free-av.com/en/download/index.html .
Avira is best & light solution for excellent overall system protection & internet security with real time updates, .

2. Malwarebytes - http://www.malwarebytes.org/ .
Malwarebytes is one of the best & effective antimalware tool out there.

3. Ccleaner - http://www.piriform.com/ccleaner/download .
CCleaner is a system optimization, privacy and cleaning tool with an effecient & most useful registry cleaner.

The Best Security combo for all types of systems.

avira free and pc tools firewall plus also free!