 Microsoft Security Essentials ( MSE ) is an antivirus software ( AV ) product that provides protection against different types of malicious software such as computer viruses , spyware , rootkits and Trojan horses . Before version 4 @.@ 5 , MSE ran on Windows XP , Windows Vista and Windows 7 , but not on Windows 8 and later , which have built @-@ in AV components . MSE 4 @.@ 5 and later do not run on Windows XP . The license agreement allows home users and small businesses to install and use the product free of charge . It replaces Windows Live OneCare , a discontinued commercial subscription @-@ based AV service , and the free Windows Defender , which until Windows 8 protected users from only adware and spyware . 
