How to denie registration when unwhitelisted char is used?
 

Hello Guys,

I would like to denie the registration when another character than
abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWX YZ0123456789_
in the username is used.

Is that possible?
If yes, how?

In the ACP go to vBulletin Options->User Registration Options->Username Regular Expression and put in an expression to match only the characters you want. I haven't tried it, but I think you'd want
^[a-zA-Z0-9_]+$

You didn't mention the space character, if you want to allow spaces you'd have to put that in too. (The help for that option has other examples).

Great help, thank you very much. Didn't know it was that easy!