Competing with paid security offerings from big-name vendors such as McAfee and Symantec, the Microsoft anti-virus product asks users to uninstall any existing anti-virus on their systems. This is not unusual, however, as multiple anti-virus products can conflict with each other.
Running on desktop Windows operating systems from XP Service Pack 2 and above, Microsoft Security Essentials anti-virus replaces Windows Live OneCare, which was discontinued this summer. The program is also designed to run in Windows XP Mode, which is the virtualized Windows XP with Service Pack 3 that will be made available free to users of Windows 7 Professional, Enterprise, and Ultimate editions.
Significantly, although offered as a home-based tool and unable to integrate with enterprise-level systems management software, Microsoft has left the door open for very small businesses to use the anti-virus software. The license agreement specifically says that it is legal to use Microsoft Security Essentials for home-based businesses.
Several other vendors also provide free anti-virus products. AVG Antivirus has a free offering designed for consumers, and so does Avast!, along with BitDefender, among others.