The usual problems of data leaks are bad enough: Compromised customer and employee privacy, lost reputation, government fines, and lawsuits. For Shell, the damage is worse, as the contact database for 176,000 staff and contractors at the firm were copied and forwarded to activists opposed to the company.

Richard Wiseman, chief ethics and compliance officer at Royal Dutch Shell, wrote to staff last week after the breach emerged.

He said: "The Global Address List, containing contact information of everyone in Shell and some contractors, joint ventures and other third parties, has been downloaded without authorisation and distributed to some external parties. We do not know who did this. We are investigating and are raising this theft of information with the relevant data protection authorities."

The company played down the security implications of the loss - it is phone and email details rather than real-world addresses.

The database went to environmental and human rights campaigners.

Those behind the leak claimed they were members of the company attempting to mount a "peaceful corporate revolution."

The email was accompanied by a 170-page covering note explaining that it was being circulated by a group of "116 concerned employees" from the UK, US and Netherlands.

Shell told Sky News the contact list was genuine but that it believed the email was a hoax.

A spokesman said: "The email was brought to our attention by an external stakeholder. We're looking into it and we do not believe it is genuine."

The cover note said the attackers wanted to "highlight the damage allegedly caused by Shell's operations in Nigeria."

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