I Just saw the notice below that Microsoft Security Essentials 2 is now available directly from Microsoft. I didn't notice it automatically updating so you will probably need to use the link below to download and install. Be aware that it will ask to restart your computer at the end of the install.
Microsoft Security Essentials is your first line of defense against virus and malware, so I highly recommend you have it installed and install this upgrade as soon as you have time. It is always easier to prevent and infection than try to remove the nasties once they get in. Having Security Essentials installed won't guarantee your protection, but it will go a long way towards preventing the most obvious infections.
Download Microsoft Security Essentials 2
Microsoft Security Essentials 2 Released, Still the Best Darn Antivirus Around [Downloads]: "
Windows: We've learned to stop worrying about antivirus software since Microsoft released their great Microsoft Security Essentials suite, but today it gets even better, improving Windows Firewall integration, network traffic inspection, and an heuristic scanning engine.
Microsoft's next version of Security Essentials is actually a pretty great update from its already-great predecessor. Microsoft's option has always been adequate at finding new malware without definitions, but the addition of an heuristic engine bumps its power up quite a bit. It may be subject to a few more false positives, but you're much less likely to get hit with malware than ever before.
It also includes some Windows Firewall integration that lets you tweak the Firewall from inside Security Essentials, as well as a network inspection feature that can inspect traffic as you browse, which is pretty neat. All in all, if you're using Microsoft Security Essentials (and why wouldn't you be?), you'll want to grab this update. Hit the link below to manually download and install the update.
Microsoft Security Essentials is a free download for Windows.