JJAntispam helps you prevent spam registration on your Joomla website by checking the spammer's signature against the Botscout spammer database. If the user that tries to register gets a positive hit, he is denied registration.
In version 1.3 if you block users you are automatically reporting them to SpamBusted. This way their IP will never bother you again.
In version 1.4 you can add an extra layer of security by checking against Botscout as well. Since version 1.4 uses Joomla transport layer for server-to-server communication, Joomla 2.5 is most recommended.
lIn version 1.9 the plugin only check against Botscout, as Spambusted is no longer available. Also, upon blocking a user the plugin verifies that user against Botscout and lets you know if it's a spammer. Optionally, it allows you to directly delete that user if so.