And the linked article clearly states why they were fired:

"The latest development occurred Monday when Google (GOOG) sent an email to all staff members describing its decision to fire four employees for allegedly violating its data-security policies. Google confirmed the contents of the email titled "Securing our data," which was first obtained and reported on by Bloomberg. The email described some of the actions allegedly taken by the fired employees, including accessing other employees' calendars and sharing information about their whereabouts with outside sources. It was sent out on behalf of Google's Security and Investigations Team."