"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," confirmed Matt Mullenweg, a founding developer of WordPress. "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 partnersí code. Beyond that, however, it appears information disclosed was limited."
As the servers also contain proprietary code from their users, Twitter and Facebook usernames and passwords and API keys, users that host their blogs on WordPress.com are advised to change all the passwords that could have been compromised - even though Mullenweg says that the WordPress passwords were stored hashed and salted using phpass - and to use different passwords for different sites.
The investigation is still ongoing, but in his replies to the comments below his post, Mullenweg said that financial information was definitely not compromised and that so far it appears that the hacker's activity was largely exploratory - i.e. not targeted.