If you use WP Super Cache, you should immediately update to version 1.4.5 as it patches a XSS vulnerability in the settings page. This version also prevents PHP object injections. In addition to security patches, 1.4.5 contains a number of bug fixes. Make sure to update your sites as soon as possible to patch the vulnerability. You can find more details on this release on Donncha Ó Caoimh’s website.