Another suggestion: Spam User
Now when is someone marked as Spam User, there are possibilities: Do nothing
Disable Post/PM permission
Disable Post/PM and unapprove posts
Unapprove posts, empty profile and ban account
Well, there could be another option (move to specified group). Although last option (... ban account) is good possibility but I want to exclude those users from Members group. When I send bulk mail to Members I don't want to send mail to Spammers. They are banned but still in Members group.