Every public school in Los Angeles has been closed in the wake of an unspecified threat:

Officials closed all Los Angeles Unified School District campuses Tuesday morning after receiving a “credible threat” of violence involving backpacks and packages left at campuses.

Authorities said they plan a search operation of all the LAUSD’s more than 900 schools. The nation’s second-largest school district has more than 700,000 students.

“I think it’s important to take this precaution based on what has happened recently and what has happened in the past,” LAUSD Superintendent Ramon Cortines said.

The move comes less than two weeks after two shooters killed 14 people in San Bernardino in what was the deadliest terrorist attack on U.S. soil since Sept. 1

Fearing the safety of schools and students, Cortines said he couldn’t take a chance, so he asked police to search all campuses, adult school and early education centers before reopening Wednesday.

Officials said the threat came in electronic form and was made to numerous but unspecified campuses. As a result, they made the decision to close them all for the day.

The Los Angeles Police Department and FBI were assisting with the threat investigation, said Los Angeles School Police Chief Steve Zipperman.

“The threat is still being analyzed,” he said. “We have chosen to close our schools today until we can be sure our campuses are safe.”

At this point, it’s unclear exactly what the nature of the threat might have been or why authorities felt it necessitated the closing of an entire urban public school system in a move that impacts nearly 700,000 students, their parents, teachers, staff, and of course law enforcement. Typically, of course, terrorists of recent vintage do not call in their threats and the information has been released so far make it sounds as if these were threats that were received by authorities of imminent action rather than an intercept of intelligence that led them to believe something might happen. In the wake of recent events, though, including not just recent terror attacks but also mass shooting incidents, it seems as though authorities could not afford to not be as vigilant as possible. Additionally, the fact that school was nearly ready to start for the day, the authorities had only a short period of time before the school day began and likely felt pressure to act quickly rather than being presented with information later in the day that necessitated evacuating schools in the wake of threats that were now deemed to be credible.

In any case, dealing with this sounds like it will be a logistical nightmare. School authorities said at a press conference this morning that they intended to search every public school for suspicious packages or material, and while this seems reasonable it’s worth noting that were talking about hundreds of schools and school buildings and it’s unclear how law enforcement would even begin to approach a search such as this. Additionally, there are hundreds of buses that transport students to and from school, and those vehicles may end up also being searched, adding to the burden on authorities.

Over on Twitter, Ross Douthat from The New York Times makes this point:

Whether it’s the right choice or a jump-at-shadows, this LA business is a bad, bad sign.

— Ross Douthat (@DouthatNYT) December 15, 2015

The point, of course, is that this decision to shut down a major urban school system over a handful of unspecified threats demonstrates both how much of a hair trigger many parts of the country are on at this point, and the dangers of overreaction to what may, after all, turn out to be a hoax. Paranoia is not a good way to deal with situations like this even in the wake of what happened in Paris and San Bernardino

Update: More from The New York Times, including the news that similar threats were received in New York City but the decision was made that to keep the schools open:

LOS ANGELES — The Los Angeles public schools were abruptly shut down and students sent home on Tuesday after the police received what officials described as a credible bomb threat against the nation’s second-largest school system, throwing into disarray the lives of millions of Angelenos — students, parents, teachers and other school staff members.

The threat was made electronically, and it was explicitly “to students at schools,” said Ramon C. Cortines, superintendent of the Los Angeles Unified School District. He said “some of the details talked about backpacks and other packages.”

But Mr. Cortines declined to say more about the nature of the threat or how it was received. The Los Angeles Police Department and the F.B.I. were investigating.

“It was not to one school, two schools or three schools — it was many schools, not specifically identified,” Mr. Cortines, wearing a gray sweatshirt, said at a news conference shortly after 7 a.m. “I am not taking the chance of bringing children any place, into any part of the building, until I know it is safe.”

Mr. Cortines and other officials said the schools would remain closed until the police and school administrators had searched every building to make sure the campuses were safe. But the logistical task involved is immense, as is the potential for chaos: The Los Angeles Unified School District has more than 640,000 students, enrolled in 900 schools and 187 public charter schools, sprawling across more than 720 square miles.

The district asked parents not to send their children to school, and ordered most employees to stay away, but many were already on their way, or even at school, when the order to close was made. Mr. Cortines and other officials said that the children were being kept out of the buildings, and asked parents to pick them up at school gates. Much of the district’s fleet of big yellow buses had already begun its morning rounds, before being told to turn back.

New York City officials said that they had received a similar threat to schools on Tuesday, but had concluded that it was a hoax. Mayor Bill de Blasio said Tuesday morning he was “absolutely convinced” that there was no danger to schoolchildren in New York.

“Our schools are safe,” the mayor said. “Kids should be in school today. We will be vigilant. But we are absolutely convinced our schools are safe.”

Police Commissioner William J. Bratton, speaking at a news conference alongside the mayor, said that threats were often made against New York City schools and htat they were assessed on a case by case basis. There was no indication, he said, that the threat made Tuesday morning was credible.

The Los Angeles school closings came as the region remained on edge after the terrorist attack in San Bernardino less than two weeks ago that left 14 people dead and 22 wounded. Over the past two weeks, there have been a number of bomb threats. But the authorities treated this one differently.

“This is a rare threat,” Mr. Cortines said. “We get threats all the time.” Though he would not elaborate on why this one prompted such a strong response, he cited circumstances like the San Bernardino massacre and other events around the world, an apparent reference to incidents like Islamic State attacks in Paris.

The difference in the manner in which the threats were treated appears to be due at least in part to the threat that in New York City the initial threat assessment was performed by the New York City Police Department whereas it was school authorities who made the initial threats in Los Angeles. In that regard, the NYPD, which has a long history now of dealing with terrorism related threats, says that it made the determination that the threats were not credible. It’s also being reported that the threats were apparently received via e-mail and appeared to have come from overseas and made references to Islamist/Jihadist terrorism. As others have noted, though, groups like ISIS and others almost never make threats, instead they tend to take responsibility after attacks have taken place. In any case, it was likely in the wake of Paris and San Bernardino, as well as the time pressures involved, that led authorities to make their snap decision. If it turns out that there was no real threat, then they are likely to be second guessed, but I’m not sure that’s the appropriate reaction under the circumstances. In this day and age, unfortunately, you can’t just assume that a phone call about a bomb in a school is being made by some kid pulling a prank, or trying to get out of a test, and it’s easier to apologize for a false alarm than be the person who received a threat before a tragedy and didn’t act on it fast enough.