The issue came to light at the University of Central Florida in Orlando after business students bought an instructors' manual and shared it with 200 classmates, the Orlando Sentinel reported.
The course's instructor used the same 300-question test bank, thinking it was secure, to create his midterm exam, and suspiciously high grades resulted.
The incident has set off debate about whether test banks are legitimate study guides or unethical leaks of potential exams.
Donald McCabe, a business professor at Rutgers University in New Jersey who studies college cheating, said the UCF case is ambiguous since students might not have known the exact questions would be on their exam.
"If they thought they were using it as a study guide, it's hard to argue they were blatantly cheating,'' McCabe said.
On Nov. 1, the UCF instructor, Richard Quinn, told students the midterm had been compromised, about 200 students had cheated by studying from the test bank and all 600 would have to take a new exam.