I find AVG Free to be a good solution. No adds, not cpu heavy,
and there are some free extras if you want them. You can trial the whole
package for a month if you want, or just take the free one permanently.
Pertinently, I havent had a virus problem I couldnt easily fix with it in years.
OOh i didn't know Bitdefender had a free version of A/V but i have been enjoying Avast: www.avast.com. The nice thing is it blocks malware even when you're just browsing the internet. I hear of users getting viruses even with their A/V up and running i assume it's because when they are clicking a site with nasties their A/V doesn't pick it up until they do a scan. But so far, besides Bitdefender, Avast has been doing well for me. Haven't tried AVG but like the posts on it in here it sounds like it runs well.