Critical security update for all Joomla! versions
Were published in 08/01/2013 security updates for all Joomla versions. The fixed issue allowed uploading malicious files to your server, allowing full files access.
Joomla 2.5.14: http://www.joomla.org/announcements/release-news/5506-joomla-2-5-14-released.html
Joomla 1.5.26: http://joomlacode.org/gf/project/joomla/tracker/?action=TrackerItemEdit&tracker_item_id=31626
(Althoug Joomla 1.5 support have been discontinued, this update is also available to tha platform, many thanks to Phil Taylor from myJoomla.com for this).
Is highly recommended to do this update, and for those sites that still runs under 1.5, do the upgrade to the new framework.