I can think of several solutions:
1. Ignore Newbies when sorting on "Last post" date. This way, Newbies can't bump threads anymore.
This is a good idea but I think that you should bump it up to Jr. Members as well.
That's probably better. My initial assumption was it takes them longer to rank up their bots, but indeed, requiring at least a Member account to bump a thread stops the spam-to-rank-up before the bots even start it.
With the screenshot I posted below you will see on this two threads I saw that Jr. Members are also part of this bumping service as well.
The posts didn't get deleted, so they fall into a different category:
That leaves them spamming without deleting posts though, but that's something for another topic.
Useless trivial posts to bump and fill a thread are also part of the "service" offered by paid spammers ("1 ETH (0.08 BTC) for 400 posts"), but catching them requires manually checking the posts. I'm not sure how often they use the same phrase, and
patrol doesn't show Jr. Members' posts, so it's much harder to automate checking.
Including the Jr. Members as well will help us shut down this kind of services more effectively.
Agreed. Let's hope Admins can implement this, I don't know if this requires a lot of work.