More than 100 applicants have been barred from Harvard's business school after they were discovered hacking into its admissions website.
Hackers tried to find out Harvard's admissions decisions
Rivals Stanford and the Massachusetts Institute of Technology have also rebuffed students who tried to find out early what decisions had been made.
The 119 Harvard hackers were barred after one of them was found to have posted instructions online.
A university spokesman described their activities as a "breach of trust".
Competition for places at leading US universities is intense. Many parents pay for personal tuition to try to give their children an advantage.
Most of the Harvard hackers, responding to an online message board hosted by Business Week magazine, were unsuccessful.
Some 32 files at MIT's Sloan School of Management were also targeted, and another 41 at Stanford, the Boston Globe reported.
Harvard Business School said those caught had failed a "moral" test.
MIT said it would re-consider candidates who applied again next year, but wanted "evidence that this was an aberration".
Meanwhile, Harvard's president, Lawrence Summers, faces a vote of no confidence next week, after suggesting that women may have less "innate ability" than men at maths and science.
However, the undergraduate faculty, which meets on Tuesday, does not have the power to sack him.
Dr Summers has repeatedly apologised for his remarks, made at a seminar in January.