Apple on Friday released Security Update 2011-005 for Snow Leopard and Lion (as well as Server versions). The update is available for download through the Software Update system preference and from the Apple Web site.

The update is described as a “Certificate Trust Policy” issue:

An attacker with a privileged network position may intercept user credentials or other sensitive information.

Specifically, the update removes DigiNotar from the list of trusted root certificates.

Fraudulent certificates were issued by multiple certificate authorities operated by DigiNotar. This issue is addressed by removing DigiNotar from the list of trusted root certificates, from the list of Extended Validation (EV) certificate authorities, and by configuring default system trust settings so that DigiNotar’s certificates, including those issued by other authorities, are not trusted.