Need help banning partial usernames

We’ve been having a problem with AnonymousFox users being created. We have logins IP restricted and iThemes confirms these accounts that somehow are getting created at never used to log in. I’m not sure how these folks are getting around iThemes (which is my underlying frustration), but given that they consistently use the name AnonymousFox followed by another short string of characters, it would be great to be able to ban a partial username. Is there a way to do this in iThemes?

Thanks in advance for your help!
Travis