Remember Microsoft Drops OneCare Antivirus Product? OneCare was Microsoft's counter to Norton's internet security products. It changed the market, because Microsoft offered protection of three computers for the price of a single license. It also was an integrated product that would automatically fix the registry, defrag the hard drive, and perform other PC maintenance in addition to providing the expected antivirus protection. Symantec responded with Norton 360, which bundled PC maintenance with protection of up to three computers.
Despite its impact on the industry, Microsoft never achieved critical mass with market share. Antivirus software is incredibly finicky, and even though Microsoft owns Windows, they had difficulty with live updates. Because I tired of working with Microsoft support personnel, I eventually uninstalled it from my computers. A recent update to Norton 360 required a support session with Symantec, so they too, are not immune to problems.
You can download Security Essentials from the Microsoft website. The Microsoft blog on the product explains that Microsoft decided to offer a free antivirus product for users that would or could not afford the other industry solutions. Different from the earlier OneCare product, this only provides malware protection. It does not offer PC tuning or backup.
What will the fallout be from Microsoft Security Essentials? explores some of the impacts of this new product. The author believes the product will be installed on computers that otherwise have no protection. He also thinks this will reduce prices and perhaps to defend against that, today's antivirus vendors will introduce larger products that do things other than antivirus. They will have to justify their pricing against, well free.