This is contrary to what Deloitte said last month when it claimed that “very few” of its clients had been impacted but that it had launched an internal review.

The hack on accounting giant Deloitte, which compromised a server that stored the email addresses of about 350 clients, may have also jeopardized emails of four USA government departments, the United Nations and some of the world’s biggest multinational corporations, according to The Guardian.

“We take any attack on our systems very seriously”, the statement said.

The hackers apparently managed to breach Deloitte’s network in October or November 2016, and the company apparently managed to detect the intrusion only in March this year. Reports of the data breach surfaced on September 25, and the global accountancy and consultancy firm initially told the Guardian that “very few” clients were affected.

“The review has enabled us to understand what information was at risk and what the hacker actually did, and demonstrated that no disruption has occurred to client businesses, to Deloitte’s ability to continue to serve clients, or to consumers”.

A major cyber-attack against the UK-based audit and consulting giant Deloitte potentially compromised emails from several USA government departments, the United Nations as well as a host of major multinational corporations.

The company stood by that position on Tuesday, telling the Guardian that “the number of email messages targeted by the attacker was a small fraction of those stored on the platform”.

The Guardian report said that it is still unclear what and how much information was taken but that the hacker had access to emails, usernames, passwords and IP addresses.