Deloitte hack hit server containing emails from across US government

Exclusive: Cyber-attack was far more widespread than firm admits, say sources, with data from as many as 350 clients in compromised system

The hack into the accountancy giant Deloitte compromised a server that contained the emails of an estimated 350 clients, including four US government departments, the United Nations and some of the world's biggest multinationals, the Guardian has been told.

Sources with knowledge of the hack say the incident was potentially more widespread than Deloitte has been prepared to acknowledge and that the company cannot be 100% sure what was taken.