This was reported over on the Windows 7 forums. MSE hasn't been updating definitions since late last week, both automatically and manually. One of the posts provides a link where one can go to download updates directly from M$. If M$ doesn't fix this soon, I'm going back to AVAST!
MSE Not Updating(45 posts)
There was a MSE Update last week which knocked some Asus Machines with Updated UEFI Bios Out of Activation.
When I called MS India to re-activate machines, they said they were aware of the issue.
Since then I've been manually updating MSE so this might be why the updates are not being pushed into machines.
Just a guess on my part as MCE is no longer automatically updating on my machines also.
I just checked my installation of MSE and it is still showing the 1.143.629.0 that I manually updated to from within MSE this morning (at least I'm not having to got to M$'s website to update). MSE automatically updates on some kind of a schedule so it won't update the instant a new update comes out so I'm leaving it alone for a day or two to see if it will automatically update.