Seven European flights searched after anonymous bomb threats

European aviation authorities are on high alert after seven flights were searched Tuesday due to a series of bomb threats.

Officials said the threats were received by email or phone and could be hard to track, the BBC reported. Some of the planes were searched upon arriving at their official destinations, although several had to make emergency landings. One flight from London Luton made an emergency landing in Budapest and was escorted by a Hungarian fighter jet. Another flight that landed in Rome was escorted by the Italian Air Force, according to the BBC.

The flights came from various places across Europe, including Copenhagen, Manchester, and Dublin, and authorities told the BBC that they’re still investigating connections between the threats. A passenger on the flight from Manchester to Murcia, in southern Spain, told the BBC that she was asked to evacuate the plane and instructed to leave all of her belongings behind. The passengers were only told later that the threat was a bomb, she said.

No explosive devices were found on any of the seven planes and each landed safely, but authorities remained on high alert Tuesday. The bomb threats followed a wave of cyber attacks on European grocery stores that hacked fridge controls, raising temperatures and spoiling food on Monday. Local Italian news outlets also reported a series of hoax bomb threats at Italian schools on Tuesday. The Europeans, a European-based think tank and activist group, said in a Tuesday statement that a total of 271 schools were threatened. The group added that 15 European countries had suffered some form of attack over the previous two days, calling it a terror war escalation on all of Europe.