i know this one but i cant remember, i just left it on simply cause when i was first installing stuff onto my computer from my old one it kept coming up that it was installing loads of random crap that i shouldnt have been installing.
but having a look at it now i would say off the top of my head that you have to goto control panel/security centre then click on "change the way Security Center alerts me" on the left hand side at the bottom and click off on there.
