An announcement posted and circulated in Mercaz Harav Yeshiva in Jerusalem in recent days warns students that a Shin Bet (Israel Security Agency) agent, masquerading as a friend of one of the eight students killed by a terrorist in the school two weeks ago, has been frequenting the school grounds and trying to glean information from students, Army Radio reported Thursday. "Keep your eyes open and avoid unnecessary conversations," urges the announcement, which asserts that the parents of one student spoke to the suspicious-looking man and understood that he was trying to obtain information about possible revenge measures. Last weekend, the Shin Bet said it had completed a probe into media reports of involvement of a rabbi from Mercaz Harav in plans to carry out a revenge attack and had found them baseless. The Shin Bet statement dismissed a report that was broadcast on Channel 1 last week, according to which a group of right-wing Jews had received permission from several rabbis to avenge the terrorist attack at the Mercaz Harav Yeshiva on March 6 in Jerusalem in which eight students were killed and nine were wounded. Public Security Minister Avi Dichter had earlier told National Religious Party MK Zevulun Orlev that neither the police nor the Shin Bet had information concerning such a plot. Security officials explained that one of the main reasons for issuing the statement was to prevent the defaming of an entire sector in society - the National-Religious camp - as well as Mercaz Harav, whose students were reported to have been involved in the alleged plot. Yaakov Katz contributed to this report.