It looks like someone has started to use Boinc to spam message threads with adverts. They are using Bots to automatically create accounts and then send posts on a large scales.

Suggestions:
Use word recognition when registering,
Limit thread access to new users (until work has been returned).
Use Blocked IP lists on the servers.
Find the source culprit or even their ISP and disconnect them.

This is an old problem, and most projects should have implemented measures against it by now.
They also create profiles with spam posts.

And one method that you missed: Don't allow user registration from the project web site, only through BOINC.

They may actually be using part of the Boinc code on the Bot, and not going through the web sites!