Microsoft released a security advisory, KB article, and software update for all supported versions of Windows that blocks RSA certificates with keys less than 1024 bits. The software update was released to the Download Center.

The update is available now to allow organizations to assess the impact of this update and to reissue certificates with larger key sizes, if necessary, before the update is sent out through Windows Update. The update is planned to be sent out through Windows Update in October 9, 2012.