Unusual number of people registering
 

I'm currently running version 3.7.3 (I know, I know, I need to upgrade).

Over the last week or so, I've had a huge number of people "Registering" on my board, typically between 20-30 at any given time, according to the Current Active Users list.

These people never actually complete the registration process, they only start it. No account is actually made. Also, there is no apparent pattern to their IP addresses (though I don't write them all down or anything).

Prior to this, I typically had two or three registrations a week. It's a bit of a niche board, nothing that would warrent 20-30 registrations in any given 15 minute period, for sure.

Am I under some form of attack here? Is there something I should know about?