If you still have a Joomla! 1.5 website, then you should update immediately to the new version 1.5.26!
The Joomla Project announces the immediate availability of Joomla 1.5.26 [senu takaa ama busani]. This is a security release. The Production Leadership Team's goal is to continue to provide regular, frequent updates to the Joomla community. Learn more about Joomla! developement at the Developer Site.