How to update Microsoft Security Essentials manually?
The database of Microsoft Security Essentials can be updated manually by following the next steps:
Verify what OS is installed (Windows XP, Vista, 7, or 8.1)
Make sure you are logged on to Windows as Administrator
Download the Microsoft Security Essentials virus and spyware definition update file according to your OS from the following pages:
Click "Run" to install the update or "Save" to save it on your computer and run it later. If installing in a Windows Vista or Windows 7 environment you should right-click the file and select "Run as Administrator" and follow the next steps.
When the definition update is running, a dialog box showing the extraction progress will appear. After finishing, you can verify the update by opening Microsoft Security Essentials, clicking "Update" and examining the virus and spyware definitions status.
If you encounter any problems you can get more information through the following page: http://windows.microsoft.com/en-us/windows/troubleshooting-update-issues