RegistrationBlocker is a system mambot thaw allows you to prevent certain usernames from being registered.

For example, you might not want someone to register by the name "webmaster" or "admin" since it could give other users wrong ideas about their identity.

One way to accomplish this is to pre-register those usernames, thus effectively blocking them. But this is quite awkward, and not very elegant.

RegistrationBlocker makes it a lot more convenient to block one or more usernames. All you have to do is to enter the usernames in the mambot's backend, one on each line.

You can even use an asterisk as a wildcard for blocking a whole range of usernames. For example, if you enter admin* in the list, you will block usernames beginning with admin like admin, administrator, administration and so forth. With *admin* you will block all names containing admin, like siteadministrator etc.

Furthermore you can limit which email addresses that can be registered. For example, a company can set up a site where only its own employees can register by specifying *@mycompany.com.

If you rather want to block certain email addresses you can do this too. For example, you can deny registrations for email providers such as Hotmail or Yahoo by inserting these lines in the prevent field:

*@hotmail.com
*@yahoo.com

Finally you can deny access from certain IP's by using the appropriate text fields. Use a * for wildcards, like 212.* to specify IP's 212.x.x.x etc. Use the Allow only field if you want to limit access to certain IP's, or the Deny access field to block those IP's. You can choose to block all access (default) or only registrations.

The usernames and email addresses are case insensitive, so webmaster will catch WebMaster as well etc.

NOTE: RegistrationBlocker works with the standard login component, Community Builder. If you use another registration component, it might not work.

(Source: http://www.kreacom.dk/mambots/registrationblocker.html)