Yesterday, Apple released various security updates for Mac OS X 10.4.3 and 10.3.9, both available in Apple's download section. These updates address a total of 13 flaws related to Apache, curl and Safari, with denial of service potential or even up to a system being compromised and taken control of. The problems, if unfixed, could cause issues elsewhere, says Apple's CTO:

A large number of applications could be affected by the vulnerability in the PCRE library used by Safari's JavaScript engine, Kristensen said. People who inadvertently click on a malicious Web site with their Safari browser could find the flaw exploited, leading to a remote execution of code on their system.
This makes the second and third patch set to be released by Apple in November, and all OS X users are advised by Apple to update. Considering how common compromised systems are and what they are used for, keeping your system up to date is more important than ever.