Apple released a security update which fixes a flaw in Sendmail (which is off by default) and includes a more robust version of OpenSSH.
You can get the update from Software Update.
The Security Update addresses a security issue in sendmail where a remote individual could gain access and control of the system. Although sendmail is off by default in Mac OS, it is recommended that all users install this Security Update. This update also includes a newer version of OpenSSL that provides improved data confidentiality by addressing a recently-discovered security issue.