Well I do not use any anti virus protection. I have 4 computers on 95% of the time and use only malwarebytes and wise care 365. I backup all my computer with acronis true image and in the last five years maybe used it twice (always had recent backups). I find that they cause more problems then they help. Especially with programs that uses key generators and find other so called "bad" infected files.
I also use sparingly wise Care365 for PC scan and that is across windows XP and Windows 7 and no problems.
Malwarebytes is the best!