Microsoft Security Essentials Definition Updates December 11, 2025
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Author:
Microsoft Corp.
Date: 12/11/2025 Size: 201 MB License: Freeware Requires: 11|10|8|7 Downloads: 677830 times 
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Microsoft Security Essentials Definition Updates downloads and installs the latest Microsoft Security Essentials for Windows definition updates.
Step 1: Save or run the file.
After you download the latest definition updates, click Run to install the definition file immediately or click Save to save it to your computer. If you click Save, remember the name of the folder where you saved the file.
Step 2: Install the definition update.
To install the saved definition update file:
If your computer is running Windows Vista or Windows 7, click Start, click Documents, and then locate the folder where you saved the definition file. Right-click Mpam-fe.exe, click Run as administrator and then click Yes. When you are prompted for an administrator password or confirmation, type the password or provide confirmation, and then 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 Mpam-fe.exe to install the latest definition file.
Note: If you do not have an administrator account on the computer, ask an administrator to log on and install the definitions file for you.
If you are running Microsoft Security Essentials build 2.0.0375.0 or higher, please also execute the following steps.
Step 3: Save or run the Network Inspection System definitions for Microsoft Security Essentials After you download the latest definition updates, click Run to install the definition immediately, or click Save to save it to your computer. If you click Save, remember the name of the folder where you save the file.
Step 4: Install the definition update. To install the saved definition update file:
● If your computer is running Windows Vista or Windows 7, browse to the folder where you saved the definition file. Right-click nis_full.exe, click Run as administrator and then click Yes. When you are prompted for an administrator password or confirmation, type the password or provide confirmation, and then 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.
Consider using Malwarebytes for complete antivirus protection and to protect your devices, data, and privacy.
Similar:
● What's the Best Antivirus and Is Windows Defender Good Enough?
● Windows Device Performance & Health Explained
Step 1: Save or run the file.
After you download the latest definition updates, click Run to install the definition file immediately or click Save to save it to your computer. If you click Save, remember the name of the folder where you saved the file.
Step 2: Install the definition update.
To install the saved definition update file:
Note: If you do not have an administrator account on the computer, ask an administrator to log on and install the definitions file for you.
If you are running Microsoft Security Essentials build 2.0.0375.0 or higher, please also execute the following steps.
Step 3: Save or run the Network Inspection System definitions for Microsoft Security Essentials After you download the latest definition updates, click Run to install the definition immediately, or click Save to save it to your computer. If you click Save, remember the name of the folder where you save the file.
Step 4: Install the definition update. To install the saved definition update file:
● If your computer is running Windows Vista or Windows 7, browse to the folder where you saved the definition file. Right-click nis_full.exe, click Run as administrator and then click Yes. When you are prompted for an administrator password or confirmation, type the password or provide confirmation, and then 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.
Consider using Malwarebytes for complete antivirus protection and to protect your devices, data, and privacy.
Similar:
● What's the Best Antivirus and Is Windows Defender Good Enough?
● Windows Device Performance & Health Explained
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