Apple has released a security update it says is designed to address a potential vulnerability in Mac OS X.
The update repairs a theoretical vulnerability in the Help Viewer application that users could have been exposed to when browsing the Web. The update is available through Software Update, and also from Apple's Web site.
Apple senior vice president worldwide product marketing Phil Schiller said: "Apple takes security very seriously and works quickly to address potential threats as we learn of them – in this case before there was any actual risk to our customers.
"While no operating system can be completely immune from all security issues, Mac OS X's Unix-based architecture has so far turned out to be much better than most."
Apple recommends all its customers install the upgrade.