Disallow spaces and special chars in usernames?

[Stabatha]

How can I set it to disallow spaces, -, _, and special chars in the username?

[Wayne Luke]

You have to use a regular expression. You can set these in the Admin CP under vBulletin Options -> User Registration Options. If you click the inline help icon, there are examples that can be used or you can find a regular expression at www.regexlib.com.

[Stabatha]

So would ^[A-Z0-9]+$ be alphanumeric characters only and not allow spaces or underscores?