The Reuters blogging platform was hacked on Friday, and a false story about an alleged interview with a Syrian rebel leader was posted. On Sunday, Reuters suffered a second security breach in which hackers gained control of one of its Twitter accounts. While Twitter hasn't commented on the latter, we have more information on the former: Reuters forgot to keep its WordPress installation updated.
Mark Jaquith, one of the WordPress platform lead developers and member of the WordPress Security Team, told the WSJ that Reuters was using "an old version" of the software that has "publicly known security issues." More specifically, the publication was using version 3.1.1. The current version is 3.4.1.
This is a textbook mistake. You should always be using the latest version of your software, especially if you're a major company that is often targeted by hackers. WordPress is, in particular, a popular attack vector for cyber criminals. While there is no guarantee that the hackers exploited an unpatched security hole in WordPress to access Reuters' blogging platform, it's more likely given this new information.