How to stop auto registration and spammer?

Hii

how can i stop auto registration and spammer? 15 auto registration in 10 min!
what can I do stop them? (I turn my site is inviteonly now)

twitman

Use the recaptcha plugin

addPlugin('recaptcha', array('private_key' => 'Key value',

'public_key' => 'Key Value'));


Go to recaptcha website to get the key

Hii

Thank you very much