SAN FRANCISCO — Credit monitoring company Equifax has been hit by a high-tech heist that exposed the Social Security numbers and other sensitive information about 143 million Americans. Now the unwitting victims have to worry about the threat of having their identities stolen.

The Atlanta-based company, one of three major U.S. credit bureaus, said Thursday that “criminals” exploited a U.S. website application to access files between mid-May and July of this year.

The theft obtained consumers’ names, Social Security numbers, birth dates, addresses and, in some cases, driver’s license numbers. The purloined data can be enough for crooks to hijack the identities of people whose credentials were stolen through no fault of their own, potentially wreaking havoc on their lives. Equifax said its core credit-reporting databases don’t appear to have been breached.

“On a scale of one to 10, this is a 10 in terms of potential identity theft,” said Gartner security analyst Avivah Litan. “Credit bureaus keep so much data about us that affects almost everything we do.”

Lenders rely on the information collected by the credit bureaus to help them decide whether to approve financing for homes, cars and credit cards. Credit checks are even sometimes done by employers when deciding whom to hire for a job.

Equifax discovered the hack July 29, but waited until Thursday to warn consumers. The Atlanta-based company declined to comment on that delay or anything else beyond its published statement. It’s not unusual for U.S. authorities to ask a company hit in a major hack to delay public notice so that investigators can pursue the perpetrators.

The company established a website, https://www.equifaxsecurity2017.com/, where people can check to see if their personal information may have been stolen. Consumers can also call 866-447-7559 for more information. Experian is also offering free credit monitoring to all U.S. consumers for a year.

In addition to the personal information stolen in its breach, Equifax said the credit card numbers for about 209,000 U.S. consumers were also taken, as were “certain dispute documents” containing personal information for approximately 182,000 U.S. individuals.

Equifax’s stock dropped 13 percent to $124.10 in extended trading after its announcement of the breach.

Three Equifax executives insulated themselves from that downturn by selling shares worth a combined $1.8 million just a few days after the company discovered it had been hacked, according to documents filed with securities regulators.

The sales, executed on August 1 and August 2, were made by: John Gamble, Equifax’s chief financial officer; Rodolfo Ploder, Equifax’s president of workforce solutions; and Joseph Loughran, Equifax’s president of U.S. information solutions.

Bloomberg News first reported the divestitures.