MSE was running on my W7 pc up to about seven days ago with no problem. So no need to panic, yet.
However, even Microsoft have admitted their anti-virus program isn't up to scratch.
Along these lines I have therefore changed my free anti-virus program to Comodo which has been running for about a week now, with no apparent problems. There are other free anti-virus programs around such as AVG and Kaspersky.
Also, check with your bank they often have anti-virus programs available for customers.