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.
If you want Windows to update your software, go to Windows Update or:
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.
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.
For antimalware and antispyware, the latest definitions are 18.104.22.168, dated 2017-27-03 11:21:47.
To download these updates:
You can find out more about our products on the Microsoft security software page.
|Antivirus and antispyware definitions (choose either 32-bit or 64-bit depending on your computer)|
|Microsoft Security Essentials||32-bit | 64-bit|
|Windows Defender in Windows 10 and Windows 8.1||32-bit | 64-bit | ARM|
|Windows Defender in Windows 7 and Windows Vista||32-bit | 64-bit|
|Microsoft Diagnostics and Recovery Toolset (DaRT)||32-bit | 64-bit|
|Forefront Client Security||More information|
|Forefront Server Security||32-bit | 64-bit|
|Forefront Endpoint Protection||32-bit | 64-bit|
|System Center 2012 Configuration Manager||32-bit | 64-bit|
|System Center 2012 Endpoint Protection||32-bit | 64-bit|
|Windows Intune||32-bit | 64-bit|
End of life for Microsoft Forefront Client Security was on July 14th 2015. Customers are encouraged to migrate to System Center Endpoint Protection.
For more information see the Forefront Client Security entry at the Microsoft Support Lifecycle site.
You can download the last available definition package, dated July 14th, 2015 for 32-bit or 64-bit. Note that this package will not include any newer updates made after July 14th, 2015, and may leave your PC unprotected.
You can also download Network Inspection System (NIS) updates for:
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:
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:
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