Slashdot article here.
"The Hardened PHP Project has announced several serious and according to them, easy-to-exploit vulnerabilities within PHP. A flaw within the function unserialize() is rated as very critical for millions of PHP servers, because it is exposed to remote attackers through lots of very popular webapplications. The list includes forum software like phpBB2, WBB2, Invision Board and vBulletin. It is time to upgrade now."