Screaming sirens serenaded Dallas residents in the early morning hours Saturday after a cyberattack set off the city’s emergency warning system. All of the city’s 156 sirens reportedly were set off more than a dozen times. Officials have not yet identified the perpetrator of the attack, the city’s Office of Emergency Management Director Rocky Vaz said, but he expressed confidence that it was someone outside the Dallas area. The city has figured out how the system was compromised and has begun working to keep it from happening again.