A software development student from York has been jailed for eight months for hacking into Facebook, claiming he wanted to help the social network to improve its security.
26-year-old Glenn Mangham admitted accessing the account of a holidaying Facebook employee in June 2011, prompting fears in the US that the company was had fallen victim to industrial espionage.
Mangham claimed he had previously assisted Yahoo and was hoping to do the same for Facebook.
He told Southwark crown court his actions were "to identify vulnerabilities in the system so I could compile a report that I could then bundle over to Facebook and show them what was wrong with their system."
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However, the prosecution disagreed with the student's "ethical hacking" defense, claiming he stole invaluable intellectual property from the social network.
Prosecutor lawyer Sandip Patel said: "He acted with determination and undoubted ingenuity and it was sophisticated, it was calculating.
"This represents the most extensive and grave incident of social media hacking to be brought before the British courts."
Presiding over the case, Judge McCreath told Mangham that his actions, which were picked up by Facebook and reported to the FBI, were not that of 'harmless experimentation.'
He said: "I acknowledge also that you never intended to pass any information you got through these criminal offences to anyone else and you never did so, and I acknowledge that you never intended to make any financial gain for yourself from these offences."
"But this was not just a bit of harmless experimentation. You accessed the very heart of the system of an international business of massive size, so this was not just fiddling about in the business records of some tiny business of no great importance."