Microsoft Security Essentials works automatically with Microsoft Update to ensure that your virus and spyware definitions are kept up to date., however if you are seeing any of the symptoms below then follow our Troubleshooting update issues for Microsoft Security Essentials documentation…
Common update issues:
You see error messages indicating that updates have failed.
When you check for updates, you receive an error message that the virus and spyware definition updates can't be checked, downloaded, or installed
Even though you're connected to the Internet, the updates fail
Updates don't automatically install as scheduled
Troubleshooting update issues for Microsoft Security Essentials