A DoS vulnerability exists in all versions of OpenSSL prior to 0.9.6k and 0.9.7c. Upgrading as soon as possible is recommended. Read the full advisory for more information.
Also, on an unrelated note, two recent vulnerabilities in OpenSSH were discovered. This is a couple weeks old now, but definitely important enough to mention here. Short story: upgrade to OpenSSH 3.7.1p2 ASAP. For more information, read the original advisory, as well as the newer portable advisory.