I like Microsoft Security Essentials but from what I have been able to find out I don't know if it is adequate. I prefer not taking chances and going with the best antivirus I can find. I like Kaspersky. And NOD32 seems to have improved and might be a good choice if somebody does not like Kaspersky. The same programs usually are at the top or near the top every year. PCWorld had AVTest check out programs and GData was number one, Norton number two, Bitdefender three, and Kaspersky four. GData seems to slow my computer down, and Bitdefender does also. I liked Norton for a while but it is still hard to get rid of it completely if you decide to remove it. Kaspersky and NOD32 will actually find stuff. Kaspersky found a component in Apple Quicktime that was not digitally signed. I don't know if it was a false positive or not but I blocked it. Quicktime still works. Could it be that that somebody managed to add something to Quicktime? The Russian Kaspersky just impresses me although I wish they had a program that was more compatible with 64 bit versions of Windows 7.
If you pick one of the top ranked programs I think you are better off. Some programs tend to be almost always near the bottom like McAffee, Norman, CA, Trustport, etc. Spending some money each year on a good antivirus program could save you a lot of money if you were attacked.