Yale University complained to the FBI on Thursday that admissions officials at Princeton hacked into a Yale Web site that was set up for prospective students.
Yale said it found 18 unauthorized log-ins to the Web site that were traced back to computers at Princeton, including computers in the admissions office.
"We're assessing the information to see if there is a federal violation," FBI spokeswoman Lisa Bull said.
The head of admissions at Princeton said the school just checked the site to see how secure it was. Princeton gained access by looking up students who had applied to both schools.
"It was really an innocent way for us to check out the security," Stephen LeMenager, Princeton's dean of admissions, told the Yale Daily News, which broke the story Thursday in its online edition.
"That was our main concern of having an online notification system, that it would be susceptible to people who had that information _ parents, guidance counselors, and admissions officers at other schools."
Marilyn Marks, a spokeswoman for Princeton, said Thursday night that an independent investigator was to arrive at the New Jersey campus Friday.
"The actions reported today by the Yale Daily News represent a serious lapse of judgment by at least one member of our admissions staff," she said. "The improper use of information provided to the university in good faith may have affected the ability of students to obtain information about their admission to Yale, something we deeply regret."
Yale said Princeton's actions violated the privacy of the students.
"We have therefore notified appropriate law enforcement authorities as well as the applicants whose Web locations were accessed," said Dorothy K. Robinson, Yale vice president and general counsel.
The Web site was activated for a few weeks in the spring so that undergraduate applicants could find out if they got in to Yale. Applicants could access the site by using their Social Security numbers and birthdates. The site included links to admissions information and data about students.
The site included a notice that only students, not parents or others, may access the site, and it warned that Yale would investigate and act on any unauthorized use.
This was the first year Yale used the Web site. The day it went online in April, more than 9,700 applicants had logged in, including 1,190 of the nearly 1,500 students who were admitted.