We've received reports from several readers (thanx, Ronaldo and anonymous) that they have seen successful exploitation of the Joomla user password reset vulnerability announced on 12 Aug (with an exploit posted to milw0rm at about the same time).  If you have not yet upgraded to 1.5.6, do so ASAP

References:

http://developer.joomla.org/security/news/241-20080801-core-password-remind-functionality.html

http://www.us-cert.gov/current/index.html#joomla_password_reset_vulnerability

http://nvd.nist.gov/nvd.cfm?cvename=CVE-2008-3681