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By default, WordPress network usernames cannot contain anything but lowercase letters and numbers. This plugin adds network options to let you include hyphens, underscores, or uppercase letters, if desired.

Furthermore, this plugin gives you the option to allow email addresses as usernames, or to allow all-numeric usernames (e.g. "1234").

Finally, this plugin lets you override the minimum length for usernames (which defaults to four characters).

To follow updates to this plugin, visit:

http://danieltwc.com/

For help with this version, visit:

http://danieltwc.com/2011/network-username-restrictions-override-1-0/