There is a program called Xrumer that spammers are using to attack forums everywhere. Many XenForo owners have seen a sharp increase in the number of spam registrations and spam posts. There are several ways to deal with this.
Very helpful… proved to be extremely useful for me to clean up close to 100,000 spam messages that appeared from 150 users over the course of three days. Spam Cleaner couldn't handle it, but this advice saved so much frustration! Thanks for writing this.