The ones that register are humans looking for a SEO boost. They've all been from countries known for that (Nigeria, India, etc.).
The bots we're seeing are crawlers. They're not bad other than taking up bandwidth and CPU resources, and not contributing to the community. The server is pretty robust by design (hardened) and I keep it up to date with the latest.
The bots can only "see" what other non-registered lookie-loos can see--so no sensitive info is exposed. But as always, like anytime you use the nets, don't post anything you don't want known. The old the internet is forever thing!