Short for Microsoft Security Essentials, MSE is a free antivirus and malware protection utility first released by Microsoft on September 30, 2009. MSE helps eliminate much of the hassle that comes with many non-free antivirus utilities.
MSE only runs on Windows XP, Windows Vista, and Windows 7. Version 4.0 and earlier was supported on Windows XP, and version 4.5 and 4.10 was supported on Windows Vista and Windows 7. MSE was discontinued on January 14, 2020, and in Windows 8 and Windows 10, MSE was replaced with Windows Defender, which is built into Windows.