Forum Spam Users!!

[thermax04]

I have vb v 4.1.3 and I found a new user registered with funny information and he registered with 2 names with the same IP but with different emails, when i searched their IP , I found a web site called stop forum spam.com and they wrote that the same IP is reported as spam (173.242.116.48 appears in our database 355 times)
And when I looked to his personal website in his registration details, I found it is for selling cloth
What is the danger of such a user registered in my forum? and how to stop such thing?

[Special Pages]

To stop it, go to AdminCP> Settings> User Registration Options and then change the option from registering from two IP's from there. Then to stop bots from registering, go to AdminCP> Settings> Human Verification Settings and change it to Question and Answer.