(CNN) -- More Long Island students were arrested Tuesday in an ongoing investigation of a college admission exam cheating scandal that has expanded to include the ACT, according to prosecutors in New York's Nassau County.
"Our office exposed a gaping hole in standardized test security," District Attorney Kathleen Rice said.
The investigation unveiled nine students who paid four men to take the SAT or ACT standardized exams for them between 2008 and 2011.
Three of the alleged test-takers were arrested Tuesday. They are Joshua Chefec, 20, a graduate of Great Neck North High School; Adam Justin, 19, a graduate of North Shore Hebrew Academy; and George Trane, 19, a graduate of Great Neck South High.
Michael Pomerantz, 18, who attended Great Neck North, is expected to surrender Monday to face identical charges, prosecutors said.
The four, who allegedly accepted between $300 and $3,600 to take the exams, were charged with scheming to defraud in the first degree, criminal impersonation in the second degree, and falsifying business records in the first degree.
The other nine who were arrested were charged with misdemeanors for paying someone to take the SAT or ACT in their place. These students, whose identities were not released because of their ages, were from both Great Neck high schools, the North Shore Hebrew Academy, and St. Mary's of Manhasset, prosecutors said.
The investigation overall has uncovered a total of 40 students who may have either taken a standardized test for someone else or paid someone to take test for them, the district attorney announced Tuesday.
Seven people were charged in late September, including Samuel Eshaghoff, 19, of Great Neck, who faces felony fraud charges for allegedly doctoring fake identifications and business records, and charging students between $1,500 and $2,500 to take their SAT exam.
A 2010 Great Neck North graduate, Eshaghoff was enrolled at Emory University in Atlanta at the time of the arrest. Rice said Eshaghoff knows the four other alleged test-takers.
"It was run like a business; there were referrals, word of mouth. A rumor mill was going around," Rice said Tuesday.
After cheating rumors emerged, an investigation found a "wide gulf" between the SAT scores and the grade-point averages for the six original students accused of paying Eshaghoff, Rice said in September.
After that first round of arrests, Rice called on the Educational Testing Service to tighten up procedures to prevent cheating, suggesting on-site test-day photographs be taken of the students and submitted along with their exam.
The ETS, contracted by College Board, which sponsors the SAT, is the non-profit that develops the tests, administers the exam at 7,000 centers, and oversees security. The ACT is provided by ACT Inc.
Rice also expressed concern about the lack of consequences for students caught cheating, as the ETS and ACT Inc. currently do not report instances of cheating to high schools, or to the colleges the students apply to.
"This system is begging for security enhancements ... and better data retention," Rice said
Thomas Ewing, spokesman for ETS, told CNN that since September, the College Board has hired Freeh Group International Solutions, an organization run by former FBI Director Louis Freeh, to review test-security protocols. Procedures will be upgraded once the review is complete, Ewing said.
He said ETS officials applaud the work of Rice, and "hope this will serve as a wake-up call to any students ... who are thinking of risking their futures with such an unethical and foolish act."
ACT Inc. spokesman Scott Gomer said the organization has been cooperating with the district attorney and will continue to do so.
Over the next few months, he told CNN, "we will implement additional test security enhancements, including immediate steps to reinforce the importance of test security for those participating in upcoming ACT tests."
Great Neck Public School Superintendent Thomas Dolan issued a statement saying the district is cooperating with the prosecutor, and he hopes this investigation will bring an end to dishonest practices that place students at an unfair disadvantage.
"The victims here," Rice said, "are the students that study well, pay lots of money to get a tutor, and no matter how hard they try, take a back seat to cheating."
CNNs Brad Lendon contributed to this report.