Deloitte hit by cyber-attack revealing clients’ secret emails

Exclusive: hackers may have accessed usernames, passwords and personal details of top accountancy firm's blue-chip clients

One of the world's "big four" accountancy firms has been targeted by a sophisticated hack that compromised the confidential emails and plans of some of its blue-chip clients, the Guardian can reveal.

Deloitte, which is registered in London and has its global headquarters in New York, was the victim of a cybersecurity attack that went unnoticed for months.