WordPress MU

Hello, recently I get a lot of automated spammers that registered into my site and tried to do link spamming.. It's so tedious that I need to delete those I expected to be spammers(since they were over 200+ accounts)..

Now each time a new user registers into the website would count him/her as a id number starting from 200+ which is a bit annoying as well.

Although, I deleted the suspected accounts in the WPMU backend, when I checked in PhpMyAdmin the wp_signups and wp_registration_log still contains the data of those that I deleted.

1.Is there a way to reset the id count back to a reasonable one?
2.Should I manually delete those in wp_signups and wp_registration_log?
3.Where can I get a free WPMU captcha?

Thanks!

Have you tried searching the forums? There is a lot of discussion. There are plugins for Mu here.

http://wpmudevorg.wordpress.com/plugins.php