Glenn Mangham, 26, a software development student, admitted infiltrating Facebook from his bedroom at his parents' house in York in northern England last year, sparking fears at the U.S. company that it was dealing with major industrial espionage.

"This was the most extensive and flagrant incidence of social media hacking to be brought before British courts," said Alison Saunders, London's Chief Prosecutor. "Fortunately, this did not involve any personal user data being compromised."

Facebook first became aware of a security breach in its internal network in April and called in the FBI. The U.S. agents established the source of the hacking was based in Britain and British police raided Mangham's home in June.

Mangham said he had previously helped search engine Yahoo Inc improve its security and wanted to do the same for Facebook. However, prosecutors rejected his explanation.

"He said he wanted a mini project and chose Facebook because of its high-profile internet presence," prosecutor Sandip Patel told London's Southwark Crown Court.

"The prosecution does not accept that the defendant's actions were anything other than malicious."

The court was told Facebook spent $200,000 in dealing with his actions, the Press Association reported.

Judge Alistair McCreath told Mangham his actions were not harmless and had "real consequences and very serious potential consequences" which could have been "utterly disastrous" for Facebook.

"You and others who are tempted to act as you did really must understand how serious this is," he said.

(Reporting by Michael Holden; Editing by Andrew Heavens)

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