Microsoft has released an update for Microsoft Security Essentials that offers performance enhancements and some new functionality within the program. Microsoft constantly works to improve the product and this is a normal/periodic update through regular update channels. As such, this upgrade is available via the Windows Update process and can be installed automatically, but if it is preferred you can also install the update using the following process:
Open Microsoft Security Essentials.
Click the down arrow located to the right of Help.
Click Check for software updates. A Windows Update window will appear.
Click Install updates.
If prompted, click Restart now. Your computer will restart and the update will install.