The company says it will no longer provide XP with security updates through Windows Update, which seems to indicate that Microsoft Security Essentials also won't update with regular virus definitions, making it nearly worthless.
Since its 2009 launch, Microsoft Security Essentials has become the number one antivirus software in the U.S. and number two worldwide. Starting with Windows 8, Microsoft rolled its Security Essentials functionality into Windows Defender and included it with the operating system.
According to Microsoft, "If you continue to use Windows XP after support ends, your computer will still work, but it might become more vulnerable to security risks and viruses. Also, as more software and hardware manufacturers continue to optimize for more recent versions of Windows, you can expect to encounter greater numbers of apps and devices that do not work with Windows XP."
Those who have a more recent version of Windows such as Windows Vista or Windows 7 won't have to worry about Microsoft ending support until 2017 and 2020, respectively.