The computer file is said to contain testimony from the woman who said she had sex with Matt Gaetz, President-elect Donald Trump’s choice to be attorney general, when she was 17.

An unidentified hacker has gained access to a computer file shared in a secure link among lawyers whose clients have given damaging testimony related to Matt Gaetz, the former Florida congressman who is President-elect Donald J. Trump’s choice to be attorney general, a person with knowledge of the activity said.

The file of 24 exhibits is said to include sworn testimony by a woman who said that she had sex with Mr. Gaetz in 2017 when she was 17, as well as corroborating testimony by a second woman who said that she witnessed the encounter.

The information was downloaded by a person using the name Altam Beezley at 1:23 p.m. on Monday, according to the person, who was not authorized to speak publicly. A lawyer connected to the case sent an email to the address associated with Altam Beezley, only to be informed in an automated reply that the recipient does not exist.

The material does not appear to have been made public by the hacker.

The documents include information that is under seal with the Justice Department, which investigated Mr. Gaetz but did not file charges, and the House Committee on Ethics, which has completed its own inquiry into the former congressman. The Ethics panel’s members are scheduled to meet on Wednesday to decide on whether to vote to release material it has gathered.

But the hacked trove of documents stems from an altogether different source: a civil suit being pursued by a friend of Mr. Gaetz’s, Christopher Dorworth, a Florida businessman. Mr. Dorworth filed the suit against both the woman who says she had sex with Mr. Gaetz when she was a minor and Joel Greenberg, an erstwhile ally of Mr. Gaetz who is serving an 11-year prison sentence after pleading guilty to federal sex trafficking charges involving the woman.

Mr. Dorworth has claimed that he was defamed by Mr. Greenberg and the woman, both of whom had told federal authorities that Mr. Dorworth hosted parties where he, they, Mr. Gaetz and others took drugs and openly had sex.

In mustering their defense, lawyers for Mr. Greenberg and the woman have solicited sworn statements from others who they say were witnesses. The 24 exhibits were attached to a motion prepared by lawyers for Mr. Greenberg and the woman in response to Mr. Dorworth’s suit.

The hacked information also includes sworn testimony from Mr. Dorworth and his wife, as well as testimony from Michael Fischer, Mr. Gaetz’s former campaign treasurer, who is also said to have attended the party. It also contains various supporting material, such as the gate logs showing who entered the property of the Dorworth home on the evening in July 2017 when the two women said the sexual encounter with Mr. Gaetz occurred.

The material apparently taken is unredacted and includes the names and other personal information of the witnesses but is otherwise said to be more damaging to Mr. Gaetz than to his accusers, according to the person familiar with the hack. The hacker had not contacted the lawyers as of Tuesday morning, and it was not clear what motive the person might have.