You can manually update your Microsoft security software by downloading the definitions on this page.
A definition is how we clean or remove a virus or other threat from your PC. When you update your definitions, you are updating your protection
against these threats.
You must have Microsoft security software installed to use these
Manually update your Microsoft security software
There are two ways to manually update your security software.
You can update by going to Windows Update or
clicking the Update button within the Update tab of your Microsoft security software.
These definitions are updated once every 24 hours.
Sometimes you might want to update more often than once a day. This can be especially helpful if a particular piece of malware just won’t go away, no
matter how many times your security software tries to clean it.
You can get the latest updates below.
Antimalware and antispyware definitions
For antimalware and antispyware, the latest definitions are: 1.163.1923.0, Dec 13, 2013 05:12 PM UTC
To download these definitions:
- Check whether your version of Windows is 32-bit or 64-bit.
- In the table below, right-click on the link that will work for your version of Windows and choose Save target as... or Save link as...
- Save the file to your Desktop.
- When the file has finished downloading, go to your Desktop and double-click the file (it will be called mpam-fe.exe or mpas-fe.exe).
- Follow the prompts to install the updated definitions.
You can find out more about our products on the Microsoft security software page.
Microsoft security software works with Microsoft Update to automatically download the latest definitions. If these automatic updates aren't working there may be an issue with your PC. You can get help fixing automatic updates below:
Some malware can also turn off Microsoft updates. In this case you might need to use the Microsoft Safety Scanner
or for more stubborn malware, Windows Defender Offline
Network Inspection System definitions
You can also download Network Inspection System (NIS) definitions for Microsoft Security Essentials, Forefront Endpoint Protection, and System Center 2012 Endpoint Protection. These definitions are designed to protect you from exploits and network infections.
The version of your Microsoft security software determines which type of NIS definitions you must download.
To determine your version:
- Open your security software by double clicking on the icon in the system tray (you may need to click the arrow to see the icon) or, in Windows 8, search for Windows Defender:
Click the arrow next to Help and choose About <Software name>:
- Your software version number is displayed at the line labelled Antimalware Client Version
For version number 4.1.522.0 and above, you must download the Network Realtime Inspection definitions:
If you have a version number lower than 4.1.522.0, you must download the Network Inspection Service definitions: