Registering Proubelm

I have been getting in the habit of checking current users on the site after I log on and been noticing that I see some new users in REGISTERING mode quite often. These folks never seem to finnish registering as I also check for new users. They also have different IP addresses. Thought maybe I had a problem with folks logging on, but I tried to log on and register as a new user, and it worked fine. What could this be? Do you think someone is trying to mess with the site?