Microsoft offers partially-tested pre-release definition updates for download before the fully-tested (released) version is available. These updates are listed below.
You can use these pre-release definitions to clean infected computers. You can also use them to protect computers that are at an immediate risk of infection. The pre-release definition update is not meant for enterprise-wide deployment.
Pre-release updates are explicitly created for malicious software threats. You should not deploy a pre-release definition update if you are not experiencing a threat for which it was explicitly created.
Note: After additional testing, certain pre-release definition updates will be released as regular definition updates. The same binary file that was used for the pre-release definition update may be used for the released definition update.
How to install the update:
The following procedure outlines how to install a pre-release definition update.
Before you begin, you must establish whether your computer is running a 32-bit version or a 64-bit version of Windows. If you are unsure what version your computer is running, refer to the following link:
How to determine whether a computer is running a 32-bit version or 64-bit version of the Windows operating system (KB827218)
Click on the link that applies to your computer:
For Microsoft Antimalware products including Microsoft Forefront products or Microsoft Security Essentials:
For Microsoft Antispyware products including Windows Defender:
- Choose one of the following options:
- If you want to install the update immediately, click Run. A file extraction box will appear, indicating the definition is installing. The box will close once installation is complete
Note: If you are installing the update on a computer that is running Windows Vista or Windows 7 and you are prompted for an administrator password, type the password and click OK. If you are prompted for confirmation, click Continue
- If you want to save the update to run at a later time, do the following:
- Click Save, and save the file in a folder
- Click Start then Run, and open the folder where you saved the update.
- Double-click the update file, and then click OK. A file extraction box will appear, indicating the definition is installing. The box will close once installation is complete.
Note: If you are installing the update on a computer that is running Windows Vista or Windows 7, right-click the file, and then click Run As Administrator. If you are prompted for an administrator password, type the password and click OK. If you are prompted for confirmation, click Continue.
If you want to use the command-line switch to install the update in quiet mode (this suppresses the file extraction dialog box), type the following command:
Note: To run this command, you must use an account that has administrator rights.
Regular definition updates are available if you subscribe to the automatic definition update mechanism in the next regularly scheduled release. You can also choose to manually update your definition library.
The latest definition updates are always available for download on our latest definitions page.