The U.S. Justice Department has opened a criminal investigation into whether top officials at Equifax Inc. violated insider trading laws when they sold stock before the company disclosed that it had been hacked, according to people familiar with the investigation.

U.S. prosecutors in Atlanta, who the people said are looking into the share sales, said in a statement that they are examining the breach and theft of people’s personal information in conjunction with the Federal Bureau of Investigation. The Securities and Exchange Commission is working with prosecutors on the investigation into stock sales, according to another person familiar with the matter.

The federal probes add a serious challenge to Equifax as lawmakers, state attorneys general and regulators scrutinize the breach that may have compromised the privacy of 143 million U.S. consumers. Equifax shares were little changed. The shares have fallen 35 percent since the breach was disclosed after the market closed on Sept. 7.

Investigators are looking at the stock sales by Equifax’s chief financial officer, John Gamble; its president of U.S. information solutions, Joseph Loughran; and its president of workforce solutions, Rodolfo Ploder, said two of the people, who asked not to be named because the investigation is confidential.

The company and the executives didn’t immediately respond to requests for comment.

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Equifax disclosed earlier this month that it had discovered a security breach on July 29. The three executives sold shares worth almost $1.8 million in early August. The company has said the managers didn’t know of the breach at the time they sold the shares.

Regulatory filings don’t show that the transactions were part of scheduled trading plans.

To run afoul of laws that prohibit insider trading, a seller has to be aware of nonpublic information, said Stephen Crimmins, a former enforcement lawyer for the Securities and Exchange Commission.

The probe will be handled by the U.S. attorney’s office in Atlanta, where the credit firm’s headquarters is located, said one of the people. A spokesman for the U.S. attorney’s office in Atlanta declined to comment on the investigation into share sales, but confirmed an inquiry into events surrounding the hack.

“The U.S. Attorney’s Office for the Northern District of Georgia is working with the FBI to conduct a criminal investigation into the Equifax breach and resulting theft of personal information,” said U.S. Attorney John Horn in a statement.

The SEC, in its preliminary probe, is looking into what executives knew and when about the data breach, according to the person familiar with that matter.

More than one-third of U.S. senators have called on the Securities and Exchange Commission, in addition to the Justice Department, to get to the bottom of whether Equifax managers violated insider trading laws when they sold stock days after the company found out it was hacked.

Separately, state and federal regulators and law enforcers are scrutinizing the company’s data security practices and its response to the breach. The U.S. Federal Trade Commission and a congressional committee with subpoena power last week joined the growing number of bodies looking into the cyberattack.

Tom Schoenberg, Anders Melin and Matt Robinson are Bloomberg writers: Email: tschoenberg@bloomberg.net, amelin3@bloomberg.net, mrobinson55@bloomberg.net