The FBI has begun an inquiry into the practices of booming daily fantasy sports websites after players of the games and lawmakers made allegations of predatory tactics and questioned the use of inside information, according to fantasy players who said they had been contacted by investigators.The FBI began contacting several prominent competitors in the contests, the players said, shortly after an employee of DraftKings, one of the two most prominent daily fantasy companies, admitted to inadvertently releasing data before lineups for the start of the third week of NFL games were locked in. The employee, a midlevel content manager, then won $350,000 at a rival site, though DraftKings said he did not have an advantage.The players said that they were interviewed by agents from the bureau's Boston office, who seemed to focus primarily on DraftKings, a Boston-based company. They also said that agents were examining whether the site encouraged and accepted deposits and bets from states where the contests are prohibited. The information under review includes a post by Jon Aguiar, an executive in charge of developing high-volume fantasy players, on a public thread informing players how to deposit funds and play in contests in states and countries where the games are prohibited.The daily fantasy sites, worth billions of dollars on paper because of a surge of investors, have exploded in popularity and this season have blanketed football game broadcasts with ubiquitous advertisements to lure more participants, who pay an entry fee, build virtual rosters of players from actual teams and win prizes, from $22 to $2 million, based on the performance of the chosen players in real games.Major League Baseball and the NBA, along with New England Patriots owner Robert Kraft and Dallas Cowboys owner Jerry Jones, are among investors in the sites, along with networks such as NBC, Comcast and Fox.The FBI agents also wanted to know whether employees of DraftKings passed on proprietary information or preyed on fantasy players in contests, according to the players.It was unclear how far the investigation had proceeded.The FBI declined to comment.DraftKings, as well as the rival site FanDuel, have acknowledged that their employees — many of whom regularly rank among the most consistent big winners — have played and won significant money on each other's sites.A FanDuel spokeswoman has acknowledged that DraftKing employees have won just less than $10 million on their site. In the wake of the scandal, they banned their employees from competing in any contests.The allegations have also raised a bevy of issues in the unregulated industry, including whether or not professional fantasy players have an unfair advantage over regular players. A recent study in Sports Business Daily found that over the first half of this year's Major League Baseball season, 91 percent of daily fantasy sports player profits were won by just 1.3 percent of the players. In fact, on average, the top 11 players paid $2 million in entry fees and made profits of $135,000 each while accounting for 17 percent of all entry fees.Many of those professionals use automated processes that let them change hundreds, if not thousands, of lineups in seconds, a decided advantage when last-minute changes are made in the real lineups of football, basketball or baseball teams.The Wall Street Journal first reported on the FBI interviews of players.The New York attorney general last week opened an inquiry into the prospect that employees of DraftKings and FanDuel, the leading daily fantasy companies, won lucrative payouts based on information not available to the public. In addition, three class-action suits have been filed alleging fraud — the most recent in Louisiana, where the operation of daily fantasy sports sites is prohibited. The plaintiff, Artem Genchanok, a New Orleans resident, said he had paid entry into DraftKings and FanDuel contests and deposited money on their websites despite the prohibition.In Washington, Rep. Hakeem Jeffries, D-N.Y., a member of the House Judiciary Committee, this week called on the panel to examine "whether permitting a multibillion-dollar industry to police itself serves the best interests of the American people," while Sen. Robert Menendez and Rep. Frank Pallone Jr., both D-N.J., held a news conference Tuesday outside MetLife Stadium, reiterating their calls on the Federal Trade Commission to implement safeguards to ensure a fair playing field.And Sen. Richard Blumenthal, D-Conn., on Monday formally called for a federal investigation into any deceptive or fraudulent practices at daily fantasy sports leagues."Consumers had no foreseeable knowledge that these companies were facilitating employees' use of proprietary data to provide themselves with an advantage when playing users on their rival site," Blumenthal stated in a letter to the Justice Department and the FTC. "If employees are using insider information to unfairly advantage themselves over others, this may constitute fraud."