Professional services giant Deloitte has confirmed it suffered a cyber attack but said “very few” clients were affected.

Attackers gained access to Deloitte’s systems through an email platform and accessed confidential data such as the private emails of clients.

The attack was discovered in March, The Guardian reported, but may have happened months earlier.

Those affected by the breach have been contacted by Deloitte. The New York-headquartered firm said it had informed Government authorities and regulators of the incident, although it did not say how many people had been affected.

It added in a statement: "Deloitte remains deeply committed to ensuring that its cyber security defences are best in class, to investing heavily in protecting confidential information and to continually reviewing and enhancing cyber security.”

Deloitte provides auditing, tax consultancy and cyber security for many of the world’s biggest banks, companies and government agencies.

The Guardian claimed that the attack was concentrated upon the US with several American government departments affected.