AUGUSTA, Ga. — A federal prosecutor said on Thursday that Reality Leigh Winner, the National Security Agency contractor accused of leaking a highly classified report, might have stolen or exposed other secrets before her arrest last week.

“This was not the first time the defendant mishandled classified information,” Jennifer G. Solari, an assistant United States attorney, said during a detention hearing, in which she described a recorded jailhouse telephone call and referred to an episode last year in which Ms. Winner placed a portable storage device into a sensitive computer.

It was not clear, either in Courtroom No. 1 or even to federal investigators, whether Ms. Winner had distributed classified information beyond a single N.S.A. report related to Russian hacking activities. But Ms. Solari said the authorities were concerned because Ms. Winner referred to “documents” during a telephone call with her mother.

“I screwed up,” Ms. Winner, 25, the first person to face prosecution by the Trump administration in connection with a leak of sensitive information, said during the call, according to Ms. Solari.