The Astros hired Mr. Luhnow as general manager in December 2011, and he quickly began applying his unconventional approach to running a baseball team. In an exploration of the team's radical transformation,Bloomberg Business called it "a project unlike anything baseball has seen before."
Under Mr. Luhnow, the Astros have accomplished a striking turnaround; they are in first place in the American League West division. But in 2013, before their revival at the major league level, their internal deliberations about statistics and players were compromised, law enforcement officials said.
The intrusion did not appear to be sophisticated, the law enforcement officials said. When Mr. Luhnow was with the Cardinals, the organization built a computer network, called Redbird, to house all of their baseball operations information — including scouting reports and player personnel information. After leaving to join the Astros, and bringing some front-office personnel with him from the Cardinals, Houston created a similar program known as Ground Control.
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Ground Control contained the Astros' "collective baseball knowledge," according to a Bloomberg Business article published last year. The program took a series of variables and "weights them according to the values determined by the team's statisticians, physicist, doctors, scouts and coaches," the article said.
Investigators believe Cardinals officials, concerned that Mr. Luhnow had taken their idea and proprietary baseball information to the Astros, examined a master list of passwords used by Mr. Luhnow and the other officials who had joined the Astros when they worked for the Cardinals. The Cardinals officials are believed to have used those passwords to gain access to the Astros' network, law enforcement officials said.
That tactic is often used by cybercriminals, who sell passwords from one breach on the underground market, where others buy them and test them on other websites, including banking and brokerage services. The breach on the Astros would be one of the first known instances of a corporate competitor using the tactic against a rival. It is also, security experts say, just one more reason people are advised not to use the same passwords across different sites and services.
Last year, some of the information was posted anonymously online, according to an article on Deadspin. Among the details that were exposed were trade discussions that the Astros had with other teams. Mr. Luhnow was asked at the time whether the breach would affect how he dealt with other teams. "Today I used a pencil and paper in all my conversations," he said.
Believing that the Astros' network had been compromised by a rogue hacker, Major League Baseball notified the F.B.I., and the authorities in Houston opened an investigation. Agents soon found that the Astros' network had been entered from a computer at a home that some Cardinals officials had lived in. The agents then turned their attention to the team's front office.
"The F.B.I. aggressively investigates all potential threats to public and private sector systems," an F.B.I. spokeswoman said. "Once our investigations are complete, we pursue all appropriate avenues to hold accountable those who pose a threat in cyberspace."