I suggest you to use the premium anti virus to protection optimazation of your system. I always use Kaspersky to protect my system. you can use AVG, Avira or panda, that all free edition.
I use BitDefender.I switched from Kaspersky to this cos this has game mode which completely stops notofications.So i dont get disturbed while playing games
I too using "Avast". It gives me an alert when any viruses is present in my system. I prefer my friends to use this.