If you google “regents exam cancelled yeshiva” (without the quotes) and scroll down a bit, you’ll find an article from the Schenectady Gazette from 1989. The previous year, a yeshiva student from Queens was charged with stealing Regents exams and a NYC paper (I think it was the Post) published the answers to the chemistry exam, saying that it wasn’t fair that some kids with money could buy the answers.
A little more googling reveals (according to the Geneva Daily Times) that in 1974, a whole bunch of exams were canceled when students at Solomon Schechter broke in and photocopied the exams.
These days, the security is tighter, but of course it isn’t foolproof.