I have used Microsoft Security Essentials ("MSE") in the past, but it tends to conflict with other virus software. When I did utilized MSE it did not catch viruses as effectively as other software. However, it was definitely better than not having virus protection. For a free software it works pretty well.
Tess- As for your comments about Norton & McAfee, I COMPLETELY agree. I have been working with computers for years and these are some of the worst programs on the market!! I also do not like AVG. I have had AVG crash too many machines in the past and I will not us this program.
Julie