Step1 Ensure that the date and time are set correctly on your PC
Open Microsoft Security Essentials.
If the error message that you received contains the code 0x80072f8f, the problem is most likely caused by an incorrect date or time setting on your PC.
To reset your PC's date or time setting, follow the steps in Fix broken desktop shortcuts and common system maintenance tasks.
Step 2
There are other things that you can do however the most easy way is to install updates manually

Manually install the virus and spyware definition updates
If you're running a 32-bit Windows operating system, download the latest updates manually at http://go.microsoft.com/fwlink/?LinkID=87342
If you're running a 64-bit Windows operating system, download the latest updates manually at
http://go.microsoft.com/fwlink/LinkID=87341.
Click Run. The latest updates are manually installed on your PC. http://go.microsoft.com/fwlink/?LinkID=87342 http://go.microsoft.com/fwlink/LinkID=87341