The security software is Microsoft's replacement for Windows Live OneCare, a for-a-fee security suite that was retired at the end of June 2009.
Microsoft offered a beta version of Security Essentials, once codenamed 'Morro', to about 75,000 users in June, but quickly stopped it when that target was reached.
Two weeks ago the company thanked beta testers for their help and said that the polished edition of Microsoft Security Essentials would ship "in the coming weeks".
"All files were properly detected and treated by the product," said Marx. "That's good, as several other [antivirus] scanners are still not able to detect and kill all of these critters yet," said Andreas Marx, one of the firm's two managers.
However, Symantec is urging PC users not to rely on the software as their only form of protection.
"The security industry has moved on from the product Microsoft is launching. Unique malware and social engineering fly under the radar of the traditional signature based technology employed by free security tools such as Microsoft's," said Con Mallon, EMEA Consumer product marketing director at Symantec.
"We believe the false sense of security provided by this tool is almost as dangerous as having no security at all.The latest generation of internet security is real-time and reputation-based, operating in real-time and not relying on a signature being produced and downloaded before the computer is protected."
Symantec also suggested that commentary from users, reviewers and testers of Microsoft's beta version indicated that "the company needs to do a lot of catching up, to even get close to the latest paid for products on the market".
Security Essentials will run on Windows XP SP2 or later, Windows Vista and Windows 7 and can be downloaded from Microsoft's site.