This is straight from Microsoft Article and its very important…..
Reports of rogue anti-virus programs have become more prevalent lately. These are programs that generate misleading alerts and false detections of malcode in order to convince users to purchase the illegitimate security software.
For example, programs such as Trojan:Win32/Antivirusxp and Program:Win32/FakeRednefed may display product names or logos in an apparent unlawful attempt to impersonate Microsoft products. These products may represent themselves as "Antivirus XP", "AntivirusXP 2008", "WinDefender 2008", "XP Antivirus", etc.
So before you try to think of doing something to protect your computer, you mite end up doing quite the opposite.See your agent for the safest way to protect yourself and only download programs that has been reviewed by popular sites and especially Microsoft.