A cyberattack at Deloitte, one of the "big four" accounting firms, may have revealed confidential client information, according to a statement from the firm.
The company believes hackers gained access through Deloitte's email server.
Deloitte is still investigating the incident, but said in a statement to CNBC that the review of the email platform is complete.
The company contacted governmental authorities immediately after discovering the attack and notified each of the "very few" clients impacted, a Deloitte spokesman said in the statement.
"Deloitte remains deeply committed to ensuring that its cybersecurity defenses are best in class, to investing heavily in protecting confidential information and to continually reviewing and enhancing cybersecurity," the spokesman said.
The firm is registered in London and has its headquarters in New York and boasts clients including Morgan Stanley, Berkshire Hathaway, Starbuck's, Boeing and Microsoft, along with global banks, media organizations and government agencies.
Deloitte offers tax services, auditing, consulting and cybersecurity advice to clients.