High Quality Content by WIKIPEDIA articles! Microsoft Security Essentials is a free antivirus software created by Microsoft that provides protection against viruses, spyware, rootkits, and trojans for Windows XP, Windows Vista, and Windows 7. MSE replaces Windows Live OneCare, a commercial subscription-based antivirus service and the free Windows Defender, which only protected users from adware and spyware. It is geared for consumer use, unlike Microsoft's upcoming enterprise-oriented product Microsoft Forefront. Symantec and McAfee, two competing antivirus vendors, responded by claiming that MSE is not as good as their own software.