Prevent usernames with extra characters

Hi!

Sorry for my English. I don't know the right term for "extra characters".

Well - I have read a few times now that there shouldn't be characters like &%$§"<>|`´#' and so on in usernamens.
I have checked the options of the registration form from CB but I cannot find anything that comes close to "forbid (those characters) in usernames". Our test users have registered nicknames that only consist of those characters / signs with no problem.

Is there any way to only allow alphanumeric characters or numbers in user names?
In Germany we are in need of ä,ö,ü, so these should be excluded from the exclusion somehow...
If not - Will using those so called extra characters be a thread to our server, website or user database?

Thanks for any help!
Christoph

Go to the cb admin panel->fields->username.
There's a field validation option where you can set your regex values to define what characters to allow/not allow.

Ah! Thank you. I was looking in the wrong places.