I'm running a public wiki (MediaWiki) on a VPS from a hosting company (a2 hosting) and I'm using reCaptcha v2 to prevent spam content.
Recently, I've noticed spam articles that have slipped by. They are all advertising links to external websites, as per usual spam. What I've noticed is that the links to the websites have all been to websites hosted on the same hosting company to me. The IP addresses that the spam has originated from has been from all over the place and show no clear correlation to one another.
I can anticipate spam that would not be caught by reCaptcha, and I would expect them to seem to originate from all over the place. But the fact that they all advertise websites on the same hosting company would seem to me to be statistically unlikely: a2 hosting isn't one of the really big companies (I believe?) and this is approximately 10 incidents so far (about 1/day for the past week or so).
What's the explanation for this? Is this reCaptcha's algorithms failing or is the hosting company at fault for misconfiguring something?
Clarification: the sites being advertised are, I believe, hosted by a2 hosting since they are using the default a2 hosting name servers. That's not conclusive, but the mere fact that they all share the same nameservers is statistically unlikely. The websites are:
- der maj oie cre am .com
- tes toe dge .net
- nut riv ano for sko lin .net
- z-v ita l .com
- pro hdg arc ini a .net
- der man uix cre am .com
- ket ope rfo rma nce plu s .net
They don't deserve any traffic, but you can check their whois records.