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Microsoft pre-release definition updates
Microsoft offers partially-tested pre-release definition updates for download before the fully-tested (released) version is available.
Latest pre-release definition version: 1.261.1595.0
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.
Install pre-release updates
The following procedure outlines how to install a pre-release definition update.
Before you begin, you need to know whether your computer is running a 32-bit version or a 64-bit version of Windows.
You can run the file immediately or save it to disk to run at a later time.
You can also use the command-line switch to install the update in quiet mode (this suppresses the file extraction dialog box). Use the following command in an administrator-level command prompt, from the location of the saved file:
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.