Apple released Security Update 2009-004 yesterday to fix an issue with the DNS Service:
By sending a maliciously crafted update message to the BIND DNS server, a remote attacker may be able to interrupt the BIND service. The issue affects servers which are masters for one or more zones, regardless of whether they accept updates[…] This update addresses the issue by properly rejecting messages with a record of type ‘ANY’ where an assertion would previously have been raised.
BIND is disabled by default in Mac OS X & Server, but if you’ve got the DNS Service enabled you’ll want to apply this update. Grab it for Leopard or Tiger Server (Universal) or pick it up via Software Update. It’s also available for Mac OS X client.