I cant believe Mechbog recommend ms securty essitail while majority of us recommans Avira AV
It has very high detection rates on
new malware (which is what counts if you're looking for prevention), has no splash screens, doesn't require as much configuration to get full protection, and works with Vista/7's UAC system to prevent unauthorized changes or disabling of protection by an exploit. AntiVir's not bad, but as a package, I think MSE has some advantages.
MSE also installs the Microsoft Update engine, if I'm not mistaken. For those with extra Microsoft software that's never gotten patched (e.g. Office or whatnot) because they've only been using Windows Update instead of
Microsoft Update, it will get people up-to-speed on that as well.