WordPress.org

Author: Linda MacPhee-Cobb

This plugin automatically bounces most bot attempts at user registration on your blog. You can also blacklist ips and email addresses to block. If an attempt is made to register by a bot that is not blacklisted that email address and ip number are automatically added to the blacklist.

This plugin creates a page under 'Manage'. On it you can blacklist ip numbers, email addresses, domains and extensions you do not want to register on your site.

The management page will also give you a list of all attempts at registration and if they were bounced and why.