Europe has been hit by a new wave of plane bombing threats. Reuters. Danish police said they were investigating threats to passengers at Copenhagen Airport. The French Prime Minister's Office reported four new bomb threats against planes flying over French territory, and that all of them landed safely. Due to a report of a bomb on board a Ryanair flight from Rome to Lisbon, a security operation was carried out after landing. The threats bore all the hallmarks of a coordinated "hybrid attack," security experts said. "The most likely assumption is that we are facing an attempt at hybrid aggression and a type of psychological warfare," said Spanish Foreign Minister Jose Manuel Alvarez, adding that Europe must be prepared for other similar challenges.