MsMpEng.exe is a process belonging to Microsoft Windows Defender Antispyware which protects your computer against Internet-bound threats such as spyware and trojans which can be distrubuted through e-mail or attack directly to the computer allowing unauthorized access to your computer. This program is important for the stable and secure running of your computer and should not be terminated.
You have to remember that this is still a "beta". Windows Defender still has a few bugs. As mastershakes mentioned, reinstalling might resolve your issue.
The following is based on an average memory usage:
Process for Defender:
8.1MB Memory usage during real time protection (background)
8.8MB Memory usage during scanning
11.2MB Virtual memory during real time protection (background)
11.4MB Virtual memory during scanning
4.5MB Memory usage during real time protection (background)
5.2MB Memory usage during scanning
9.2MB Virtual Memory during real time protection (background)
9.4MB Virtual Memory during scanning
If you are worried about its high usage. You could just set the service to disabled and start it whenever you want to perform a scan. So whenever you need to perform a scan just start Windows Defender and services and disable them upon scan finish. but this defeats the purpose of having it run in the background
Ep, glad to see you come back and tidy up...did want to ask a one day favor, I want to enhance my resume , was hoping you could make me administrator for a day, if so, take me right off since I won't be here to do anything, and don't know the slightest about the board, but it would be nice putting "served administrator osnn", if can do, THANKS