I'm sorry but I don't trust anything from microsoft, especially their antivirus programs. I've worked on three systems now with this protection suite and all three were infected up to their eyeballs.
If you want decent antimalware that actually
works check out
Avira Antivirus or
Avast! Antivirus for active scanners. I've personally used both, but at the moment prefer Avast! for no particular reason. Add
ZoneAlarm Free Firewall to the mix and you have a solid antimalware system without paying a dime. For those that are especially paranoid check out
Malwarebytes Antimalware Scanner; it's a system scanner with the sole purpose of finding and eliminating malware programs. It won't protect your system from being attacked like Avast! or Avira will, but when it happens this beauty is a deadly secret weapon for fighting back. I'm personally running all three programs (Avast, ZoneAlarm, Malwarebytes) and aside from a couple rogue downloads that I picked up in *cough* questionable areas (Avast! caught it anyway and prevented it from latching in) I have yet to experience any major attacks on my system in the near 6 years since I built it.
On another note holy crap man, talk about long download time!! I'm sitting on 7 hours until it completes. No way you could add this to Megaupload or somewhere with a slightly higher download rate for free users?