Harvard Business School (HBS) Dean Kim B. Clark pledged yesterday to reject applicants who used a hacker’s tip to check their admissions status online nearly a month early.

In a statement, Clark called the prospective students’ actions “unethical at best—­a serious breach of trust that cannot be countered by rationalization.”

Clark wrote that any applicants found to have hacked into the site “will not be admitted to this school.”

Last Wednesday, an anonymous individual posted instructions on Business Week Online’s technology forum explaining how applicants to several top graduate schools—including the business schools at Harvard, Carnegie Mellon, Duke, Stanford, Dartmouth, and MIT—could view the status of their admissions applications early.

An HBS spokesman said that over 100 applicants hacked into the site during the nine-hour period before the loophole was closed. While some were able to view preliminary decisions, most found only blank files, the Boston Globe reported Saturday.

All the schools use a common online application and decision notification system called ApplyYourself.

Len Metheny, chief executive officer of ApplyYourself, said he would visit HBS today to debrief staff there on the hacking.

Representatives of several of the other schools have also said they will reexamine the applications of prospective students who used the hacker’s instructions to check on their application status.

James A. Gray, a spokesman for Duke University’s Fuqua School of Business, said that one applicant at the school had tried to hack into the system. Gray said the action would be a “black mark” on the applicant’s record.

“It’s pretty obvious...that this was not the standard way to find out if you’re admitted to [business school] or not,” Gray said. “I’m not a lawyer, but I certainly know right from wrong.”

He said the applicant had not been able to access his admissions information because the school had an additional firewall on its site.

Mike Laffin, a spokesman for the Tepper School of Business at Carnegie Mellon University, said that applicants to the school who checked their admission status early would be rejected.

“If any of our applicants did get into this system we would not admit them to this MBA program,” he said. “We’re trying to determine what happened.”

Laffin said he had been told that two applicants had checked the status of their applications early. He added, however, that the school would verify that the applicants accessed the system before taking any action.

Metheny said that schools could check on their own who had accessed the privileged information.

“Our ApplyYourself system has the ability for schools to check the status of certain activity within the system,” he said.

In a statement, Derrick Bolton, the director of MBA admissions at the Stanford Business School, called for applicants who accessed their admissions information to come forward.

“Business schools teach students to make decisions and to be accountable for those decisions,” he said. “We hope that the applicants who accessed their accounts might contact us to explain their behavior and to take ownership for their actions.”

In the current round of admissions, HBS will officially notify applicants of its decision on March 30.

—Staff writer Joseph M. Tartakoff can be reached at tartakof@fas.harvard.edu.