US lawmakers attacked credit report giant Equifax after the company revealed that 143 million US customers may have had their information stolen.
Two Congressional committee chairmen said they would hold hearings into the data breach, one of the biggest ever reported in the US.
Several state prosecutors also said they would investigate.
Shares in Equifax dropped by almost 14% on Wall Street as investors weighed up how the incident would affect the firm.
Rep Jeb Hensarling, who leads the House Financial Services Committee, said: “Every breach leaves consumers exposed and vulnerable to identity theft, fraud and a host of other crimes, and they deserve answers.”
That committee and the commerce committee will hold hearings.
Also on Friday, attorneys general in New York, Illinois, Massachusetts, Connecticut and Pennsylvania said they were opening state investigations into the data breach.
Credit card details
The breach puts people at risk of identity theft and other forms of fraud.
Equifax said it found signs of unauthorised access to data including names, addresses and Social Security numbers at the end of July.
Customers in the UK and Canada had also been affected. The hackers also accessed credit card information from more than 200,000 people.
The company set up a website for people to learn if they were among those whose information had been accessed and sign up for free credit and identity theft monitoring.
The website required people to waive the right to sue, drawing outrage. The company later clarified that the clause only applied to people who signed up for the credit monitoring services, and not to actions arising over damage suffered due to the data breach.
Equifax handles data on more than 820 million consumers and 91 million businesses worldwide, according to its website. It performs services such as credit checks, employment verification and identity theft monitoring.
Recent massive data breaches
- Yahoo one billion records exposed
- 711 million online spambot accounts
- 412 million Friend Finder Networks
- 200 million US voter records