Why are dots in username & groupname no longer allowed?

[lists at benjamindsmith.com (Benjamin Smith)]

Try this one: 

chown -R c.smith.users /home/c.smith

See the problem? 

-Ben 

On Friday 30 December 2005 03:48, Remco Barendse wrote:
> For some strange reason I am no longer able to create groupnames or 
> usernames (with useradd and groupadd) that contain a dot.
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