Distro build hosts and distro package maintainers might not be a bad guess. Depends on whether getting this shipped was the final goal. It might have been just the beginning, part of some bootstrapping.
I guess one must ask El Reg to write about it. I think that might have been how it got solved a couple years ago when comp.lang.c and others were affected by this [1].
Currently, at least mozilla.support.seamonkey (not a USENET group, but from news.mozilla.org - which was shut down, but whose archived content would certainly be useful) is in that state at Google Groups. And yes, IIRC the only SPAM in recent times in that group had been posted via Google Groups...