We have had quite a few readers write and ask why the Microsoft Security Center shows an alert that Microsoft Security Essentials is turned off, even though it is running normally. Most of the time this happens after a major update, but it can happen at any time.
If this happens to you, it’s easy to fix. This is all you have to do:
1. Open Microsoft Security Essentials
2. Click “Update” (even if MSE shows it’s up-to-date)
3. Let MSE run through the update cycle and when it’s done, the Security Center alert will disappear.
So instead of reinstalling MSE to fix this issue (which some sites recommend), just follow the instructions above and everything will be running perfectly again.