Deny string patterns in usernames on registration (eg 1276908856)

[Belgrael]

Hey there,

I realise there is the ability to deny usernames with certain words in them but I have a bot creating user accounts with sets of numbers as the username at present.

Is there a way to deny usernames based on this type of pattern? (ie. more than 4 numbers in the username)

Thanks in advance.

Di