We have been diligently reviewing logs and records about the break-in to determine the extent of the information exposed, and re-securing avenues used to gain access. We presume our source code was exposed and copied. While much of our code is Open Source, there are sensitive bits of our and our partners’ code. Beyond that, however, it appears information disclosed was limited.
And threatpost.com has comments about it:
This isn't the first time Automattic has found itself in the crosshairs. In March, the company was the target of a large denial of service attack. Wordpress installations hosted on infrastructure managed by Network Solutions were also the target of attacks in April, 2010 that redirected thousands of Wordpress blogs to malware-laden drive by download Web sites.
It is important, in the above article, to notice that it's not the open source part of wordpress that has been stolen, but some not-to-be-disclosed code. And it seems that it is the case only because of the use of weak passwords.