The hack is thought to have happened earlier this year and will come as blow to a firm that claims to offer clients the best available cyber security.
“In response to a cyber incident, Deloitte implemented its comprehensive security protocol and began an intensive and thorough review including mobilising a team of cybersecurity and confidentiality experts inside and outside of Deloitte,” a spokesperson said.
“As part of the review, Deloitte has been in contact with the very few clients impacted and notified governmental authorities and regulators.
“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,” the spokesperson added.
According to the Guardian report, the attack was US-focused and was regarded as so sensitive that only a handful of Deloitte’s most senior partners and lawyers were informed.