You know what they say about "great minds", Sébastien, and we apologize for the worry Brian. We spent the better part of yesterday morning digging into these spam posts to determine who they came from and where, so we wanted to hold off replying until we had more data.
First, we confirmed the impact was limited to spam posts and didn't extend past the community itself. Second, this was not a compromise of any kind. Instead, the spammer was registering one-off accounts with verified emails, then pasting in their pre-written content. We have taken steps to ban/block this poster along with every IP address associated with them and their accounts and so don't expect too much of this in the future. But, we'll be especially diligent and got rid of it as soon as we can.
Unfortunately, spam posts happen from time to time and while we already have some implemented solutions, we intend to add some additional ones in addition to making it easier to handle reported posts and posters. To Sébastien's point we plan on implementing some things like additional captcha areas and other settings administrators can manage to further restrict who can post and how often.