Microsoft has released the final version of Security Essentials, a basic suite of tools to detect and prevent viruses, spyware, and other forms of malware. A public beta was offered back in June to the first 75,000 people to download the software. The free suite is now available to anyone running Windows XP, Windows Vista, or Windows 7, provided that your system can pass the Windows Genuine Advantage check.
I'm sure the suits at McAfee, Symantac, AVG, and others are not too happy about Microsoft's latest venture into their territory.