A vital security update will be released tomorrow (Thursday Oct. 22nd), and Joomla! users are advised to apply it immediately. Read the announcement on the Joomla! news feed.
What's it all about, and why the secrecy?
Reading between the lines, someone has discovered and reported a vulnerability in Joomla! core code that could allow hackers access to any sites using the CMS. This vulnerability may not yet have been discovered by anyone with malicious intentions, and giving away further details before the fix was released could make matters worse by publicising it to hackers.
What do Zipfish site owners need to do about this?
Nothing: we will apply the patch as soon as it's available.