“Both companies have strong policies in place to ensure that employees do not misuse any information at their disposal and strictly limit access to company data to only those employees who require it to do their jobs,” the statement said. “Employees with access to this data are rigorously monitored by internal fraud control teams, and we have no evidence that anyone has misused it.”

Industry analysts said the episode could leave the leagues open to further criticism that they are too loosely regulated.

“The single greatest threat to the daily fantasy sports industry is the misuse of insider information,” Mr. Wallach said. “It could imperil this nascent industry unless real, immediate and meaningful safeguards are put in place. If the industry is unwilling to undertake these reforms voluntarily, it will be imposed on them involuntarily as part of a regulatory framework.”

Already, there has been intensifying discussion on social media and among lawmakers over whether daily fantasy games are pushing the boundaries of an exemption in a 2006 federal law that has allowed them to operate. The law prohibited games like online poker but permitted fantasy play, deemed games of skill and not chance, under lobbying from professional sports leagues. The games are legal in all but five states.

But because Congress did not foresee how fantasy sports would explode, one member, Representative Frank Pallone Jr., Democrat of New Jersey, recently requested a hearing to explore the relationship between fantasy sports and gambling. “I really think if they had to justify themselves at a hearing they wouldn’t be able to,” Mr. Pallone said in a recent interview.

The data that DraftKings acknowledged was released by its employee, Ethan Haskell, showed which particular players were most used in all lineups submitted to the site’s Millionaire Maker contests. Usually, that data is not released until the lineups for all games are finalized. Getting it early, however, is of great advantage in making tactical decisions, especially when an entrant’s opponents do not have the information at all.