This page explains how updates work and where to get them.
If you don't already have Microsoft security software, or you want to reinstall it, see our software download page.
If you're using Windows XP, see our Windows XP end of support page.
For a list of the latest updates see the change log.
Windows will automatically download and install updates once a day for you.
If automatic updates aren't working there might be an issue with your PC:
You can also force a download of the latest daily update. This is the same as when Windows automatically downloads the update, and can be useful if you aren't always connected to the Internet or haven't turned your PC on for a few days.
If you want a more recent update (usually uploaded to this page within the last three hours), you can manually download and install it.
Force a daily update
If you want Windows to update your software, go to Windows Update or:
- Open your Microsoft security software.
- Click the Update tab.
- Click the Update button.
Because these updates change once a day, the definition version might be different to what is shown on this page, even after you've clicked the Update button.
Usually, updating once a day gives you a good level of protection, and it prevents us from constantly updating your software and interfering with how you use your PC.
Sometimes you might want to update more often. This can be helpful if you have hard-to-remove malware, Windows update isn't working properly, or you aren't always connected to the Internet.
Manually download the latest updates
If you need to get the latest updates available, you can download and install them from here.
For all Microsoft security software, you will need to download the antimalware and antispyware updates.
Antimalware and antispyware updates
For antimalware and antispyware, the latest definitions are 18.104.22.168, dated Sep 16, 2014 09:55 PM UTC.
To download these updates:
- 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, mpas-fe.exe, or mpam-feX64.exe).
- Follow the prompts to install the update.
You can find out more about our products on the Microsoft security software page.
Network Inspection System updates
You can also download Network Inspection System (NIS) updates for:
- Microsoft Security Essentials
- Forefront Endpoint Protection
- System Center 2012 Endpoint Protection
These updates are designed to protect you from exploits and network infections, and are automatically included in other Microsoft security software.
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 8.1, search for Windows Defender:
- Click the arrow next to Help and choose About:
- 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: