DALLAS City officials said a lack of encryption of the signal transmitted to 156 warning sirens led to the sirens being hacked and activated from last Friday night into Saturday.

City spokesperson Sana Syed told ABC affiliate WFAA-TV that technicians had not set the system to use encrypted comms. The sirens triggered intermittent false alarms for about an hour and a half until officials deactivated the system early Saturday morning.

The sirens went through about 15 cycles of a 90-second siren activation, Rocky Vaz, who heads the city’s Office of Emergency Management, said at a news conference.

“We shut it down as quickly as we could, taking into consideration all of the precautions and protocols we had to take to make sure that we were not compromising our 156-siren system,” he said.

Dallas city manager T.C. Broadnax told reporters the hack was based on wireless communications, not remotely through computer software.♦

“The issue was with how we transmitted our information and we’ve worked to close those gaps,” Broadnax said. ♦