Don't want to cry wolf but maybe something in this ? ........There are some posts regarding MSE ( KB3140527 ) - showing up in Windows Update - upgrading MSE to v126.96.36.199 From AskWoody forum : February 25, 2016 at 3:39 pm UH-OH! Woody, tell fellow reader RD to REMOVE/UNINSTALL Microsoft Security Essentials v188.8.131.52 [KB3140527] IMMEDIATELY! This new version of MSE is causing major problems on Vista/Win7 computers as noted in this MS forums page, and possibly rendering MSE program ununsable. Revert back to the previous version (184.108.40.206) by using System Restore or use the older version of the MSE installer to install the older version. AVOID INSTALLING Microsoft Security Essentials version 220.127.116.11, folks! v18.104.22.168 of MSE is NOT yet available as a standalone download from the MSE web site and still offers the more stable v22.214.171.124.