Equifax Inc, a provider of consumer credit scores, said on Thursday a hack exposed the personal details of potentially 143 million U.S. consumers between mid-May and July.
The company's shares were down 5.4 percent in after-market trading
The company said criminals had accessed details including names, social security numbers, and, in some cases, driver's license numbers.
In addition, credit card numbers of around 209,000 U.S. consumers and certain dispute documents with personal identifying information of around 182,000 U.S. consumers were accessed, the company said.
Equifax also said personal information of certain UK and Canadian residents were also hacked.
The Atlanta-based company it would work with UK and Canadian regulators to determine the next steps.
Equifax, which discovered the unauthorized access on July 29, said it had hired a cybersecurity firm to investigate the breach.
The company said there was no evidence of a breach into its core consumer or commercial credit reporting databases.
The breach could be one of the biggest in the United States.
Last December, Yahoo Inc said more than 1 billion user accounts was compromised in August 2013, while in 2014 e-commerce company EBay Inc had urged 145 million users to change their passwords following a cyber attack. http://reut.rs/2wMNxrT (Reporting by Yashaswini Swamynathan in Bengaluru; Editing by Sriraj Kalluvila)