Apple has just released Security Update 2011-005 for OS X. This is a small update that targets an issue related to fraudulent security certificates issued by DigiNotar.
From the release notes:
Impact: An attacker with a privileged network position may intercept user credentials or other sensitive information
Description: 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.
Direct links to the update can be found below: