“It ain’t what you don’t know that gets you into trouble. It’s what you know for sure that just ain’t so.”

I agree. We've been slowly changing from McAfee to Microsoft Security Essentials at work for the last 4 months and it's worked really well. Its fast, has a small footprint and you can't beat free. I've read that it doesn't do a great job on behavioral detection, but I think that's why it has that small footprint, it's not using processing power 24/7. Highly recommended.