The bad part is that Microsoft has its own antivirus, called Microsoft security essentials. Any Free antivirus is better
I use the following to stay clean.
(1) Microsoft Security Essentials
(2) Superantispyware
(3) Malwarebytes Anti Malware
(4) CCleaner
(5) ATF cleaner
Currently testing Comodo Av ( the free one) to replace as many of the above as I can