I think an understanding of how this actually works may be in order. These spambots aren't enterprising scouts who have decided FTB is "the market" for them; the spambots are the result of a webcrawler script that pinged off the metadata on this site and went "oh, that's a XenForo install, throw the XF bots at them until we get a confirmed registration and then deploy that".
As for who is making money off this, note that the bots posting may not in fact belong to the snake oil salesman of the week, but to somebody who is renting them out for SEO (Search Engine Optimization) and link purposes. That's right, we've gotten meta enough that SEO snake oil is being sold to literal snake oil salesmen. Snake oilception, if you will. Our intrepid buddies with the black hats aren't actually giving a damn if the ads stay here, we're just part of a blanket list that's trying to fudge PageRank and other metrics by building a bajillion "organic" links. We're just collateral in a carpet bombing exercise; they aren't necessarily going for getting people on-forum to click the link so much as they're building the links and keywords on a bunch of sites overall, which is a big part of the game of SEO. Obviously somebody somewhere is making enough money to pay all of this down the chain, but I don't think the expenses are particularly onerous; this is the age of cloud computing and botnets, after all, and no doubt all manner of illegitimate "borrowing" deals with the "hard" costs.
You can tell these are SEO-centric bots because:
- They create multiple accounts and post across all of them rather than just mashing "New Thread" in rapid succession. Blanket "true" spam posting, where a single account or a couple accounts create posts as fast as the forum allows, is ineffective because the search engine weighing heuristics know enough to recognize this kind of spam when they see it and will penalize the links in these cases.
- They create new threads rather than reply to existing ones. This is because the thread title in most forum softwares use the H1 header tag, which is given weight in determining valid search terms. You do that when you're building up search terms that you'll best match in a search engine.
- The content reads like keyword bingo interspersed with conversational-looking text. Heuristics are "best guess" and "good enough" kinds of things, and the search engine bots know enough to ding walls of keywords; what they have a harder time of, though, is dealing with something that looks like an actual sentence, even if it is gibberish to a human reader. Neither the spambots nor the search engine bots are passing any Turing Tests here, but as one makes a better mousetrap the others work out better methods around it.
These behaviors are newer, SEO-centric behaviors in spambots. A decade ago, before the SEO industry really took off, the name of the game was in fact to advertise products and make you click their link through sheer inertia. Those bots would put their crap in replies as well as new threads and just didn't take much care beyond putting out there BUY MY STUFF. E-mail spam tended and still tends to either be in the school of "fake hook so you'll open the mail" and "trash text because if you don't view this text as trash you're dumb enough to be my audience", but forum spam didn't require such "sophistication" until people got all worked up over SEO.
We do occasionally get an old school spambot here, though. Usually from India of all places (in my experience the SEO bots are Russian or Vietnamese in ultimate origin, but that's a matter of where I've bumped into them administrating forums elsewhere). Last wave of those we had was back in January or so, IIRC.
The best method to deal with the bots, as outlined, is to keep them out in the first place. That said, any given CAPTCHA or Q&A-type system generally has a shelf life of three to six months, so yes, they do penetrate. XenForo's 1.4 release, which is currently in RC and will probably be released in the next couple of weeks if not sooner, has a pretty nifty honeypot system to confound bots. Unfortunately I don't think we're going to see that update here as I think we're version-frozen pending the final word on going over to Cobalt in the future.
The next layer is to make them unable to post in the first place; keep in mind that the suggestion to put a wait period on making your first post is not really a functional one, as many of these bot runners will in fact implant a score of accounts and come back to them three or six months later to use them. One strategy I've found to be very effective is to put a post threshold on using URL and IMG tags (the bots log in, spam away at trying to post and never actually make the post because it fails), but alas, part of the purpose of this forum is in fact handling bug reports (which can involve pastebin links and screenshots), and our audience is young or not net-savvy enough to grok a rule like that (just the demographics, there's also a part of the membership that thinks the announcement threads are for posting about every damn thing they can think of instead of taking two seconds to scroll downward).
Expecting intelligence from the bots or their runners? Nah. Not worth the time investment. For giggles I once left a forum up with open registration for about 18 months; when I checked in on it it was chock-full of bots replying to each other and everything. Wasn't even logical because I'd wired nofollow into the URL tags (instructs the search engine spiders to not bother following the chain or scoring it), but again, intelligence isn't something to expect here, we're really just a sliver of collateral damage in the greater carpet bombing of the internet with this crap. =)