Install the latest Microsoft Security Essentials definition updates for a 32-bit or 64-bit computer

Download the latest Microsoft Security Essentials updates for your PC:

For a 32-bit system | For a 64-bit system
How to determine whether your computer is running a 32-bit version or 64-bit version of Windows

You can install the definition file immediately, or save it to your PC first.

• Click Run to install the definition file immediately.
• Click Save to save the file to your PC. Make sure you remember the name of the folder where you save the file.

To install the definition updates from a saved file:

1. Click Start, click Documents, and then locate the folder where you saved the definition file.
2. Right-click mpam-fe.exe, click Run as administrator, and click Run. You might be asked for an admin password or to confirm your choice.

Note: If you don't have an administrator account on the PC, ask an admin to sign in and install the definition file for you.

If you are running Microsoft Security Essentials build 2.0.0375.0 or higher, you also need to download the following Network Inspection System definitions:

For a 32-bit system | For a 64-bit system
How to determine whether your computer is running a 32-bit version or 64-bit version of Windows

You can install the definition file immediately, or save it to your PC first.

• Click Run to install the definition file immediately.
• Click Save to save the file to your PC. Make sure you remember the name of the folder where you save the file.

To install the definition updates from a saved file:

1. Click Start, click Documents, and then locate the folder where you saved the definition file.
2. Right-click nis_full.exe, click Run as administrator, and click Run. You might be asked for an admin password or to confirm your choice.

Note: If you don't have an administrator account on the PC, ask an admin to sign in and install the definition file for you.

Additional resources:

• Microsoft Security Essentials website
• Support for Microsoft Security Essentials
• Microsoft Security Essentials in Microsoft Answers