Thread creation limit

I noticed that we have a lot of spammers that suddenly show up, spam, and then disappear. They are really annoying and I'm sure it takes time to delete their thread. So, I suggest adding a limit to how many threads can be created by a new user. For example, if the user is new, maybe allow only 2 threads to be created each hour by that user. Maybe have a trial period of 1 week and then remove the limit.