Why do allies spy on each other?

Summary: Allies spy on each other. The French broke into our diplomats' hotel rooms and sifted through luggage, Israel has tried to infiltrate spies into the Pentagon, Mexico stole White House BlackBerry devices, and Germany broke into the email communications of both diplomats and journalists. But why? Read on.

http://www.zdnet.com/why-do-allies-spy-on-each-other-7000022476/?s_cid=e540&ttag=e540