Airline bomb threats on Twitter have disrupted at least sixteen flights in the past five days, prompting new concerns about aviation security — and the way pranksters can cause serious trouble with social media.

Since Saturday at least 20 different U.S. passenger planes have been targeted by bomb threats on Twitter, and federal authorities say even more threats were delivered via social media during that same period but were not publicized.

At least eight threats were posted on Twitter Tuesday from three different accounts.

One account issued threats against six separate planes, and American flight from San Francisco to Chicago, a Southwest flight from Chicago to Charlotte and four different Delta flights. The same account tweeted a threat against the San Francisco FBI office at 9 p.m. PT.

A second account targeted an American flight from Los Angeles to Chicago with a tweet that said “We are ISIS.”

On Jan. 19, a Delta Airlines flight was evacuated at John F. Kennedy International Airport after receiving a bomb threat. On Saturday, fighter jets escorted two planes to Atlanta’s airport after bomb threats were published on Twitter. The following day, a Delta Airlines flight from Los Angeles to Orlando, Florida, was diverted to Dallas/Fort Worth International Airport for the same reason, NBC News reports.

Airlines won’t comment on how often it happens, and the FBI, which is investigating, won’t say who may be tweeting. But it’s clear Twitter has given pranksters and terrorists an easy way to cause chaos.

The problem is growing.

“We’re seeing these new threats. In terms of the quantity of (online) threats we’re seeing now, you just haven’t seen it,” said Glen Winn, former head of security at Northwest Airlines and United Airlines and an instructor at the University of Southern California School of Aviation Safety and Security.

Twitter Response

Twitter spokesperson Nu Wexler said the company does not comment on individual accounts for privacy and security reasons, and referred NBC News to Twitter’s guidelines for law enforcement requests, which are published online. The guidelines say that Twitter “reserve(s) the right … to suspend or terminate users” and the right to disclose information to law enforcement when the company believes it is legally necessary.

FBI Investigates Spike In Terror Threats Against US Airlines

Authorities have received more than 50 threats directed at U.S. airlines since Jan. 17 when a flight between Atlanta and Raleigh received a bomb threat, a U.S. official said. At least 20 of those have been recorded since Saturday on Twitter.

FBI spokeswoman Laura Eimiller said Tuesday night that “all threats are taken seriously and will be investigated.”

“We are continuing to investigate these threats with our law enforcement and airline partners as we do with all stated threats,” an FBI spokesman told media. “Threats of this nature can and do result in costly responses from a multitude of law enforcement and airport entities and greatly inconvenience travelers. Individuals responsible can be prosecuted federally.”

How serious is an online threat?

“In the history of aviation sabotage, I don’t believe there’s ever been a threat called in where there’s actually been a bomb,” said Douglas Laird, a consultant who is a former security director at Northwest Airlines, in an interview to USAToday.

Still, airlines refer all threats to their security divisions, which evaluate their credibility based on confidential criteria, Laird said. Depending on the merit of the threat, a flight could be diverted to the nearest airport, so it could be searched with bomb-sniffing dogs, he said.

Airlines are required to report any security threats to a plane that is in or headed for the USA to the Transportation Security Administration.

“They make a judgment call as to whether they should take it seriously or whether there’s not complete information to act on,” said Jeff Price, associate professor of aviation management at Metropolitan State University in Denver. “They take all threats seriously, but they have to decide whether they should respond and take it to another level,” such as diverting the flight.

He says the response is based on how specific the threat is – whether it names an airline, a flight or a destination. “The more specific things get, the more you have to respond,” he said.

The investigations are looking for online “footprints” of the people who sent the threats, Price said.
“Probably the biggest question people ask is, ‘Why such a serious response? Isn’t there a way to tell if there’s (an actual threat) with all our technology?'” Price said. “It is a balance. You don’t want to land every plane that gets a bomb threat. But you want to err on the side of caution. It’s always going to be a judgment call.”