Since January of this year, U.S. Immigration and Customs Enforcement agents have arrested approximately 250 immigrants who were enrolled at a fake university in Detroit that the Department of Homeland Security had created.

Eight recruiters, who had unknowingly worked with undercover agents posing as officials at the sham University of Farmington, were indicted in January after the university was revealed to be a mass sting operation. The U.S. government accused the recruiters of helping at least 600 immigrants use the school to remain in the country unlawfully.

According to the indictments reported by the Detroit Free Press and the Detroit News, the immigrants, most of whom are Indian, allegedly arrived in the U.S. legally through student visas, then transferred to the University of Farmington to obtain jobs in the U.S. and extend their stay.

“Since the school did not offer courses or confer degrees, the enrollees were simply using the F-1 program as a pay-to-stay scheme,” ICE said in a statement to the Detroit News.

The agency’s officials told the Detroit News that their fake universities offer a “unique perspective in understanding the ways in which students and recruiters try to exploit the nonimmigrant student visa system.”

Rahul Reddy, a lawyer for several of the arrested students, told the Free Press that government officials had “trapped the vulnerable people who just wanted to maintain [legal immigration] status.”

“They preyed upon on them,” he said.

Correction: A previous version of the story incorrectly described the students as “undocumented.” The students had legal documents upon their arrival in the country.