Fifteen Chinese citizens conspired to take college entrance exams on behalf of others or paid to have that done for them so they could obtain student visas, federal prosecutors said Thursday.

The newly unsealed indictment contends the alleged conspirators scammed tests run by Educational Testing Service and the College Board — such as the Scholastic Aptitude Test, or SAT.

The alleged scheme involves test-takers and students who benefited from tests administered since 2011. Investigators weren't saying which, or how many, schools the students may have entered fraudulently.

Six named in the indictment were identified as students who paid up to $6,000 to have others charged take the tests. Five defendants were test-takers, including Han Tong, 24, who flew to California from Pittsburgh to take an SAT test for one person, the indictment says.

The precise role of the other four defendants — three of whose names remained under seal — was not clear, though the final named defendant allegedly helped with a fake passport.

The test-takers "impersonated others, and those others were able to use the fraudulent test scores to obtain F1 visas," U.S. Attorney David Hickton told The Associated Press.

F1, or student, visas allow foreign citizens to remain in the United States while they're enrolled in American colleges or universities.

With the investigation ongoing, Hickton wouldn't say whether other students also benefited or how many people were involved.

The test-takers allegedly used fake passports that contained the students' personal information, but a picture of the test-taker substituted for the student, the indictment said.

Authorities didn't say how they learned of the alleged fraud.

Siyuan Zhao, 24, one of the students who allegedly benefited from the scheme, was arrested Thursday in Boston and prosecutors planned to ask a magistrate to jail him at least until he can be brought to Pittsburgh. Tong and the 10 others whose names were publicized were being mailed summonses to appear in court soon.

The suspects face charges including conspiracy, counterfeiting passports, mail and wire fraud. The fraud counts each carry up to 20 years in prison; 10 years for counterfeiting passports; and five years for conspiracy.

Court records don't list defense attorneys for any of the suspects, and the AP could not immediately locate phone numbers for them.