While Microsoft Security Essentials has gotten mostly glowing reviews so far, some users are still hesitant to install it. One thing holding up some users is Windows Update. You can't update your Security Essentials definitions automatically if the Windows Update service is disabled. And while keeping your system fully patched is a necessity, not everyone wants to allow Windows to do it for them - they prefer the going manual route.

Fortunately, Microsoft knows this. After all, Security Essentials is based on Forefront - their enterprise antivirus product. And in the enterprise it's common practice to install updates manually. To that end, Security Essentials definitions can be downloaded as a standalone executable from Microsoft. They're available from the Malware Protection Center where you'll also find the current defs for Forefront and Defender.
Download the .exe yourself, run it, and your Security Essentials is up-to-date! Better yet, set up an app like Ketarin to handle scheduled downloads for you or use the MSE Update Utility. This a simple app that updates Microsoft Security Essentials when Windows Update is disabled. Windows Update service is responsible for frequently updating MSE. But once it is disabled via Group Policy Editor, MSE won’t update anymore. Download: MSE Update Utility Installer, MSE Update Utility Zipped