WASHINGTON — The international hackers group known as Anonymous turned the tables on the F.B.I. by listening in on a conference call last month between the bureau, Scotland Yard and other foreign police agencies about their joint investigation of the group and its allies.

Anonymous posted a 16-minute recording of the call on the Web on Friday and crowed about the episode in via Twitter: “The FBI might be curious how we’re able to continuously read their internal comms for some time now.”

Hours later, the group took responsibility for hacking the Web site of a law firm that had represented Staff Sgt. Frank Wuterich, who was accused of leading a group of Marines responsible for killing 24 unarmed civilians in Haditha, Iraq, in 2005. The group said it would soon make public “mails, faxes, transcriptions” and other material related to the case, taken from the site of Puckett & Faraj, a Washington-area law firm. A voluminous 2.55 gigabyte file labeled as those files was later posted on a site often used by hackers, Pirate Bay.

Regarding the conference call, an F.B.I. official said Anonymous had not in fact hacked into it or any other bureau facilities. Instead, the official said, the group had simply obtained an e-mail giving the time, telephone number and access code for the call. The e-mail had been sent on Jan. 13 to more than three dozen people at the bureau, Scotland Yard, and agencies in France, Germany, Ireland, the Netherlands and Sweden. One recipient, a foreign police official, evidently forwarded the notification to a private account, he said, and it was then intercepted by Anonymous.