HI this is chirag.
if you are willing to purchase Anti-Virus protection software, I recommend you to buy Latest McAfee Antivirus Suite including firewall.. It is the no. 1 Virus spywares, trojan, phising, and other malware and security Protection suite.
You may find more info on this from the following web site.
You may download a trial version to try before purchase from the following web site.
I hope the above info is helpful. If you have additional concerns regarding Microsot products also, please write back to us, I would be glad to assit you further.
Microsoft Support Professional