Apple has rolled out a patch to fix a particularly nasty vulnerability in the domain name service, BIND. THe company's Security Update 2009-004, recommended for all Mac OS X users, fixes a flaw that could let a remote party interrupt the Domain Name System service.
BIND has previously been the target of hackers, most notably a major vulnerability exposed by security expert Dan Kaminsky in 2008 that was later patched by Apple and other software vendors. On the upside, while BIND is included in OS X (both server and client editions) it's not enabled by default.
Still, a little extra security's never a bad thing, so go ahead and grab the patch. It's available for Tiger client (PowerPC and Intel), Tiger server (PowerPC and Intel) and Leopard from both Apple's support download site and via Software Update.