As the FBI and Scotland Yard conducted a conference call last month on their investigation of an international group of hackers, the discussions were being secretly monitored -- by the hackers themselves.

Anonymous, as the hacker group calls itself, Friday released the 16-minute recording that took place on Jan. 17, as well as an e-mail obtained by the group that contained the conference dial-in number and pass code.

The breach was one in a growing string of exploits by Anonymous and affiliated hacker groups that have targeted government and corporate organizations largely for political purposes.

“Other than the fact it’s not al Qaeda, it’s the worst-case scenario that the target of your operation is listening in on your call,” said Michael Sussmann, a former federal prosecutor and partner at Perkins Coie law firm.

Also Friday, Anonymous announced it had stolen 2.6 gigabytes of e-mail from a law firm that represents a Marine who oversaw troops accused of killing of 24 unarmed Iraqi civilians in Haditha, Iraq in 2005. The Marine pleaded guilty to negligent dereliction of duty; he will serve no jail time.

The first several minutes of the call between the FBI and Scotland Yard consist of banter between an FBI agent and a jocular Scotland Yard detective, making cracks about cheese and the McDonalds in the Pentagon. On the call the agents discuss timing of the prosecution of Ryan Cleary, a teenager from Wickford, England arrested last year in a probe of LulzSec. That group has claimed responsibility for disrupting the CIA Web site and hacking into the Web site belonging to the U.S. Senate, among other activities.

In the recording, a Scotland Yard detective reports on the status of the case against Cleary and another hacker and said that the British agents were willing to “set back” arrests of other hackers at the request of the New York FBI office. He discussed how the British prosecutors were trying to accommodate the FBI’s need for more time — about eight weeks — and to do so in a way “that won’t look suspicious.”

In the call, the FBI thanks Scotland Yard for its aid. “We’re here to help,” the detective replies, adding that Scotland Yard had made mistakes, too.

The transatlantic conference call between the FBI and Scotland Yard proceeded despite internal warnings by some agents that the calls needed to be secured, according to a person familiar with the breach and who spoke on the condition of anonymity to discuss the sensitive matter.

But FBI officials pointed out that the call was not classified and that no bureau computer systems were breached. Investigators believe the hackers obtained the e-mail from breaching an external personal account, which is a crime, said an FBI official, who was not authorized to speak for the record.

The FBI issued a statement Friday saying: “The information was intended for law enforcement officers only and was illegally obtained. A criminal investigation is under way to identify and hold accountable those responsible.”

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View Photo Gallery: A day after many Web sites participated in a protest against the SOPA anti-piracy bill, the Justice Department announced it was shutting down file-sharing site over piracy violations. Soon after, Anonymous took credit for shutting down the federal agency’s Web site. Here’s a look at other cyberattacks the informal hacking group has claimed credit for.