No one is sure exactly how many SAT, GRE and English-proficiency exam takers are using imposters in the U.S., but law-enforcement officials believe they could be more active than test administrators and security experts once thought possible. “Hiring test-taking proxies has been a widespread practice in China for a long time,” says Terry Crawford, who runs a video interviewing service called Initialview, which helps colleges, including Stanford, Duke, Georgia Tech, NYU, and Columbia, vet overseas applicants. “With so many Chinese students wanting to study in the U.S., it’s natural that these fraudulent practices are spreading here, where security is comparatively low.”

Last spring, Zou, her boyfriend, and 13 other current and former U.S. college students from China were arrested and last month pleaded guilty in Pittsburgh for their part in the scheme. Most will be deported. Zou’s lawyer couldn’t comment on her case because she hasn’t yet been sentenced. “During our investigation, it became clear that the scope of the scam is very broad,” says David Hickton, the U.S. attorney for western Pennsylvania. Although he says he doesn’t expect his investigators to make more arrests, “The networks that we uncovered are obviously meant to serve a much larger group than these 15 students.”

The vast majority of the 300,000 or so Chinese students who enroll in U.S. colleges each year earn their admissions credentials legitimately. Like their American counterparts, most prepare for the SAT, GRE, and GMAT by downloading study guides and past tests, which are made available to the public by the testing agencies. They use free online tutoring resources like Khan Academy, too. Like high-school students in the U.S., many Chinese students also pay hundreds and even thousands of dollars to be tutored for admissions tests to U.S. colleges and graduate programs. In China, as in the U.S., tutoring companies promise to teach their pupils specific content and test taking “tricks” that will boost their score on test day. Wealthy Chinese families also hire college-admissions agents to help their son or daughter negotiate the unfamiliar and complex college application process in the U.S. Indeed, Chinese students often come from wealthy families, and for more than a decade, colleges across the country have welcomed applications from overseas because these students are willing to pay additional fees on top of full tuition and rarely request or are given financial aid.

Obtaining a test-taking proxy to sit for an exam, though, takes the concept of test prep to a new and sometimes criminal level. According to law-enforcement officials, the scam works like this: College hopefuls or their college-admission agents contact a broker online who obtains some basic biographical information from the student—such as gender and age—and details about their appearance. Then, for a fee, the broker finds a test-taking proxy, called a “gunman,” who will be able to pass for the applicant. The gunman sends his or her photo to the broker. Some brokers simply prepare a fake passport using the applicant’s biographical information and the gunman’s photo. Other brokers actually create a photo simulation by taking the photograph of the applicant and a photograph of the test imposter and creating an amalgam of the two. The brokers charge the customer a fee based on the test, the location where it is being given, the gunman’s travel costs, and the score the college hopeful wants to obtain. Using the fake passport, the gunman takes the test. The customer only pays the broker if their hired gun achieves the test score the college hopeful is looking for.