BlogsWeek.com

“We have prepared two new releases - Plone 2.5.1 and Plone 2.1.4 - with default policy improvements to counter the spam attacks that some Plone sites have been a victim of lately. This is a required upgrade for all Plone sites, please be a responsible administrator and update your sites as soon as possible.”

For details, including a full explanation of how to clean the site if you have been affected by the spammers, please refer to the release announcement.