Joomlablog

A security exploit has been found in Mambo and Joomla. Not all sites can be defaced/hacked however it is a threat that you should take seriously.

An Official patch has been made available which works on Mambo 4.5.2 and Joomla. The Joomla patch will upgrade your site to Joomla 1.0.4 as well (Over 90 other fixes)

You should upgrade as soon as possible.
http://www.joomla.org/content/view/498/74/
Also if you are running the commercial SEF Advance from sakic.net then you need to upgrade this ASAP too.
Joomla! 1.0.4 [ Sundial ] is now available on the forge for download here. This is a Security Release, which means it contains fixes for six Security Vulnerabilities.
1.0.4 is available as a Full Package, which contains all Joomla! files and a Patch Package which contains only the files that have been changed by the Security work conducted.
1.0.4 Changelog
1.0.4 Version Information
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Wichtig! Bitte auf Joomla 1.04 upgraden. Es wurde ein Sicherheitsloch entdeckt. Es mögen zwar nicht alle Joomlaseiten betroffen sein - aber sicher ist sicher!
Auch wenn Ihr SEF Advance von sakic.net benutzt, ist es notwendig upzudaten. Nähere Informationen dazu hier.