The compromise is believed to have occurred due to the leak of an SSH key from a developer who legitimately had access to the machines in question, and was not due to any vulnerability or code exploit within FreeBSD.
No part of the base FreeBSD system has been put at risk and at no point has the intruder modified any part of the FreeBSD base system software. However, the attacker had access sufficient to potentially allow the compromise of third-party packages. No evidence of this has been found during in-depth analysis.
On Sunday 11th of November, an intrusion was detected on two machines within the FreeBSD.org cluster. The affected machines were taken offline for analysis. Additionally, a large portion of the remaining infrastructure machines were also taken offline as a precaution.
We have found no evidence of any modifications that would put any end user at risk. However, we do urge all users to read the report available at http://www.freebsd.org/news/2012-compromise.html and decide on any required actions themselves. We will continue to update that page as further information becomes known. We do not currently believe users have been affected given current forensic analysis, but we will provide updated information if this changes.
As a result of this event, a number of operational security changes are being made at the FreeBSD Project, in order to further improve our resilience to potential attacks. We plan, therefore, to more rapidly deprecate a number of legacy services, such as cvsup distribution of FreeBSD source, in favour of our more robust Subversion, freebsd-update, and portsnap models.
More information is available at http://www.freebsd.org/news/2012-compromise.html