Banning Members?

Hello,
I believe there is a computer spamming my site, creating memberships automatically. Is there a way to have a captcha installed or something that could ban a particular IP so that it doesn't happen? (or other solution)
thanks,
Pierre
I believe there is a computer spamming my site, creating memberships automatically. Is there a way to have a captcha installed or something that could ban a particular IP so that it doesn't happen? (or other solution)
thanks,
Pierre