#!/usr/bin/ruby
require "P4"
p4 = P4.new
p4.parse_forms
p4.connect
p4.run_users.each do
|u|
user = p4.fetch_user( u[ "User" ] )
puts( user[ "User" ] ) unless user.has_key?( "Password" )
end

Above program is useful when you have p4 security level set to 0.

However, 0 is not recommend practice and you can increase the p4 server authentication process by setting up following command..

p4 counter -f security 1 or 2 or 3

for more info...refer p4 counter and seclevel in manuals