Disable strange user names?

[Darakir]

I have my forum linked with a other stuff, and I really need to disable strange symbols in the registration, since the other stuff I have can't handle that.
Can I modify this myself somehow, or is there a mod that already does this?

I really want them to have just A_Z, a-z and 1-9.

[Darakir]

Would a regexp work?

[Merjawy]

you can enter anything you don't want used in registration in
Settings >> Options >> User Registration Options >> Illegal User Names

Or make use of
Username Regular Expression

[Darakir]

Regexp worked fine.

[Merjawy]

If you use English only yeah..