Problem with bots/spammers

[lawstudenthub]

I appreciate that there are topics on this issue, but I was hoping for a perspective specific to my situation. My forum is lawstudenthub.co.uk, and it's a pretty quiet forum; however, I keep seeing numerous users online, and numerous registrations. I have had issues in the past before with spammers registering and posting adverts (they seem to be human rather than bot, unless anyone believes to the contrary?). I have tried adding (and then changing) custom question on registration, but to no avail.

For instance my current legend looks like this:

There are currently 28 users online. 17 members and 11 guests
ABrookfie, AIdv, AYDY, CI47, CKPV, ECarman, EXQCX, FMcMurray, H9597, LCopley, M75O, RShackelf, RStillman, S96R, TFollett, TMcnulty, TPrado

Most, if not all, of these users are spammers.

Any advice? Do these seem like bots or human spammers?

Thanks