If you ever meet problem while trying to download definition updates for Microsoft Security Essentials (or MSE), or if you are not having any internet connection, you can download latest Microsoft Security Essentials update offline. Here’s how to do it.
Click on Start, then type
msinfo32 in Start Search and press Enter. Locate Windows system architecture type next to the System Type line. If you see x86 then you have Windows 32-bit edition. If you see x64, then you have Windows 64-bit edition.
Download latest Microsoft Security Essentials definition update file
For Windows 32-bit (x86-based) version running Microsoft Security Essentials, click here.
For a 64-bit version of Windows running MSE, click here.
How to manually install Microsoft Security Essentials latest definition updates
After downloading the update, copy it to the PC that needs it. Right-click on the saved
mpam-fe.exe(for 32-bit) or
mpam-fex64.exe(for 64-bit) file, and then click Run As Administrator.
If you are prompted for an administrator password type the password and press Enter to continue. For UAC confirmation, click on Continue to install the update (Windows XP users need to just double-click on the downloaded file to install the update). Wait while the definition files are installed.
Update: If you are running Microsoft Security Essentials build 2.0.0375.0 or higher, please also execute the following steps. Download the Network Inspection System definitions for Microsoft Security Essentials from here. After downloading, run the
nis_full.exe to install the definition immediately, or save it for later updating your computer which is offline.
Follow the instructions below to install the
nis_full.exe definition update
If your computer is running Windows 7 or Vista, right-click on the
nis_full.exe, click Run as administrator, and then click Yes. When you are prompted for an administrator password or confirmation, type the password. If you receive UAC confirmation, allow it. Wait while the definition files are installed.
If your computer is running any other Windows operating system, you must be logged on as an administrator to install the latest definition file. Browse to the folder where you saved the file, and then double-click nis_full.exe to install the latest definition file.
Source: Microsoft Support