If you have already installed Microsoft Security Essentials final on one of your Windows machines that has no internet connection and looking for a way to update the virus definition updates, here is a quick and easy solution.
Although Microsoft clearly states on the Microsoft Security Essentials system requirements page that an Internet connection is required for installation and to download the latest virus and spyware definitions, you can still update the MSE offline. Of course, you need a computer with Internet connection to download the offline updates!
Once you install MSE on a machine, it will try to update the virus and spyware definition. If the machine is not connected to the Internet, it will display “Microsoft Security Essentials wasn’t able to complete the virus and spyware definition updates. Make sure your computer is connected to the Internet and try again” error.
How to update Microsoft Security Essentials Offline:
Step 1: First you must know whether Windows XP, Windows Vista, or Windows 7 is running in a 32-bit or a 64-bit operating environment. You can find it easily by opening system properties (use Windows + Pause/Break key to open system properties).
Step 2: Next, download the offline definition updates for MSE from Microsoft:
Just save the file on a USB stick so that you can connect the USB stick to the offline machine and then update MSE.
Step 3: If you are on Windows 7/Vista, right-click on the downloaded file and select Run as administrator. If you are prompted for an administrator password or for confirmation, type the password or click Continue. And if you are on XP, simply, double-click on the file and click Ok.
Step 4: You will see file extraction dialog box for a while. After the file extraction dialog box closes, open MSE, and click Update to verify that the virus and spyware definitions have been updated.
Step 5: You are done!