An identity-theft ring in Puerto Rico stole the personal data of 7,000 children and was selling it in the U.S., the FBI said.

Members of the ring broke into dozens of schools in the U.S. island territory to steal birth certificates and Social Security card numbers, the special agent in charge of Puerto Rico for the FBI, Luis Fraticelli said Tuesday.

Authorities have seven people in custody and are seeking one more, according to Fraticelli.

Authorities told reporters that some members of the ring were illegal immigrants from the Dominican Republic who sold the data to countrymen seeking to enter the U.S. illegally.