Colleges and universities across the country remained tense on Wednesday, with several reporting incidents.

In San Francisco, officials evacuated and shut down the University of California’s Hastings College of the Law Wednesday afternoon after a threat was posted on an Internet discussion board, according to The San Francisco Chronicle.

Nell Jessup Newton, the dean of the law school, wrote in an e-mail message to students and employees that they would be required to show identification when entering any law school buildings from now on, and visitors would have to sign in.

At the University of Minnesota’s Twin Cities campus, eight buildings on the East Bank of the Mississippi River were evacuated after a bomb threat was received. Classes in the buildings were canceled for the rest of the day. But according to the university’s Web site, nothing unusual was discovered during thorough searches of the buildings.

In California, campus-police officers and Federal Bureau of Investigation agents investigated a threat to San Diego State University but decided late Wednesday that it was a hoax. In an online statement, university officials said the authorities “strongly believe they have identified the person responsible.” Earlier, administrators said they had been warned that the institution might “be targeted for violent acts” similar to those at Virginia Tech.

Officials at Colorado State University at Fort Collins evacuated a dormitory after a man with a criminal record threatened to jump from the roof, the Associated Press reported. The man, believed to be unarmed, surrendered after about two hours and was arrested.

At Lewis and Clark College, in Portland, Ore., the police detained a student wearing an ammunition belt as “a fashion accessory,” according to the AP.

A 20 year-old student at Boston University was arrested Tuesday morning after allegedly threatening to murder a young woman and others, according to a Boston CBS affiliate. Police said the student, Andrew Rosenblum, sent an instant message to a 19 year-old Wheelock College student threatening to kill her, another female student, and “everybody you love.”

“It’s going to be VT all over again,” the message reportedly said.

The woman, who had dated Mr. Rosenblum, reported the incident to local police, and Mr. Rosenblum was arrested at his parents’ home in Needham, Mass.

In Boulder, Colo., the AP reported that a student at the University of Colorado at Boulder was arrested Tuesday following remarks he made during a class discussion of the Virginia Tech shootings.

Police identified the student as Max Karson. They said he had scared his classmates by saying that he could understand why someone would kill 32 people. Witnesses also told police that Mr. Karson was angry about many things, and that they were afraid of him.

Mr. Karson’s father told the Boulder Daily Camera said that his son’s remarks has been misinterpreted, and that the arrest was a violation of his son’s First Amendment rights. The newspaper said Max Carson was a junior at the university who was “known for his controversial newsletter.” — Lawrence Biemiller and Elizabeth Farrell