Vodafone illegally accessed the mobile phone records of Fairfax investigative journalist Natalie O'Brien to find the sources of her story, according to a leaked email.

O'Brien, an award-winning reporter for The Sun-Herald, broke a story in 2011 about a major security lapse which saw the details of millions of Vodafone customers, including their names, home addresses and credit card details, available online with widely used and shared generic passwords.

Under terms of the deal, Sky would acquire all of the shares in Vodafone NZ for a total purchase price of $NZ3.44 billion ($3.24 billion). Credit:Glenn Hunt

On Saturday, The Australian published the contents of an email written by Vodafone Group's then head of fraud Colin Yates detailing his concern that the "call charge records and text messages" of O'Brien, then a Vodafone customer, had allegedly been accessed.

"If the issue relating to breaching the reporter's privacy by searching her private call records and text messages gets into the public domain, this could have serious consequences given it is a breach of the Australian Telecommunications Act," Mr Yates wrote in an email intended for Vodafone global corporate security director Richard Knowlton in 2012.