I myself actually use Microsoft security essentials and malwarebytes, making sure to keep both updated . when just playing this game i turn it off. i always have it on for web browsing etc. it amazes me how many web pages these days have those sneaky little bugs such as .Trojan.Clicker.W7,or the malicious websites add-ons which is what probably happened to Flench . I myself dont believe Microsoft security essentials is a totally safe virus protector but it is free and both will work together with seminally no conflict.
It is my belief that a persons web browsing habits are what gets them into the most trouble . the above clicker virus was detected on my computer after letting someone use my system while i was away.