The files, mostly from the 1990s, included such personal information as addresses, medical records and Social Security numbers, the New York Daily News reported Friday.
"This information would be considered a treasure trove by any identity thief," security consultant Rob Douglas told the newspaper.
The files were found in Dumpsters outside a back entrance to the law firm of Frenkel Lambert Weiss Weisman & Gordon. The law firm mostly represents the insurance and banking industries.
"I am totally freaked out. How could my information be dumped on a street?" said a 44-year-old woman whose Social Security number and medical records were among the documents left along the street.
The newspaper noted that under New York law, businesses must dispose of private information in a safe manner. Richard Lambert, a partner at the law firm, said they recently began cleaning out their old files for a June 1 move.
"We hired a licensed and bonded company to deal with the disposal of our files in a proper manner," Lambert said. "We are investigating this issue."