For something that's free MS security essentials is a damned good real time anti-virus scanner that's pretty good at picking out a lot of potential threats a long with a whole bunch of others stuff that might have been identified as a threat but don't pose any real threat at all in relative terms. In which case you still have the option to ignore it if indeed you do feel you do know better.

Security essentials not working? - Symptoms

If all you're getting is the screen above no matter what you do then its basically a little screwed. I'm not quite sure how it happens but sometimes security essentials gets in a way where its unable to turn on the real time viral scanner and update feature.Try uninstalling and re-installing the security essentials software.

If that doesn't work you can contact MS support and they will walk you through a pretty elaborate way of sorting it in order to get security essentials up and running again which does take some time.

However, if like me you want it out of the way and sorted right now try this...

1. Completely uninstall security essentials.
2. Go to the start menu and use the "search programs and files" to find the "msconfig" app. Scroll down and select Registry Editor and then click the "Launch" button.

3. The registry editor window should now be open.  Click "Computer" to make sure you can search from the root tree folder.

4. At the top click "Edit" from the menu bar and select "Find...".

5. Another box should now open.

6. In the box labelled "find what:" type in "security essentials" The registry editor should now start to look for all entries containing the term "security essentials". Once it finds the first entry it will stop and highlight it. Delete it.

7. Continue the search by clicking "edit" and select find next. Doing this will save you the trouble of having to retype it all out again. It should now find and highlight the next entry. Delete it. Keep repeating this process until it says its finished.

8. Restart your computer and re-install security essential, update it and it should now work. You're done.