If you are still using Microsoft security essentials, you should not be. Even microsoft themselves have said it should not be used, as it is not anywhere close to as effective as others are.
http://www.howtogeek.com/173291/goodbye-...arty-antivirus/
AVG Free is very good these days, among others.
http://www.howtogeek.com/173291/goodbye-...arty-antivirus/
AVG Free is very good these days, among others.