Once Windows 7 reaches end-of-support (EOS) on January 14, 2020, Microsoft will also stop updating Microsoft Security Essentials (MSE) for Windows 7.
Companies who purchase Windows 7 Extended Security Updates (ESU) will not receive special treatment, and they'll have to switch their antivirus app.
In an ESU FAQ page published earlier this month, Microsoft said it has no plans to continue supporting MSE as part of ESU.
We were told the reason is that MSE was never included with Windows 7, and is not considered a core OS component.
MSE is a free antivirus program that Microsoft has made available to its users since Windows XP, but MSE was always provided as a separate download.
MSE was gradually phased out as Microsoft started shipping Windows Defender as the default antivirus in Windows 8, and later.
MSE will continue to work on Windows 8 and later; however, very few users use MSE on recent Windows editions, mainly because they already have Defender installed.
And there are few users who bother installing MSE these days, since it's an inferior AV compared to the much more powerful Defender, considered today one of the best antivirus products on the market.