Microsoft Security Essentials ( MSE ) is a free antivirus software created by Microsoft that provides protection against viruses , spyware , rootkits , and trojans for Windows XP ( x86 MSE replaces Windows Live OneCare , a commercial subscription-based antivirus service and the free Windows Defender , which only protected users from adware and spyware . Microsoft Security Essentials ( MSE ) is a free antivirus software product created by Microsoft that provides protection against different types of malware such as computer virus , spyware , rootkits and trojan horses for Windows XP ( x86 ) , Windows Vista , and Windows 7 ( both x86 and x64 ) . Microsoft Security Essentials replaces Windows Live OneCare , a commercial subscription-based antivirus service and the free Windows Defender , which only protected users from adware and spyware .