By Claire Ballor, Robert Wilonsky and Tom Steele

Dallas officials blame computer hacking for setting off emergency sirens throughout the city early Saturday.

Rocky Vaz, director of Dallas' Office of Emergency Management, said all 156 of the city's sirens were activated more than a dozen times.

Officials don't know who was responsible for the hacking, but Vaz said "with a good deal of confidence that this was someone outside our system" and someone in the Dallas area.

The city has figured out how the emergency system was compromised and it's working to prevent it from happening again, he said. It's a "very concerning" issue that Dallas has never faced before.

Although Vaz said identifying who sounded the sirens will be like "finding a needle in a haystack,"  Mayor Mike Rawlings said authorities will "find and prosecute whomever is responsible."

"This is yet another serious example of the need for us to upgrade and better safeguard our city's technology infrastructure," Rawlings said. "It's a costly proposition, which is why every dollar of taxpayer money must be spent with critical needs such as this in mind. Making the necessary improvements is imperative for the safety of our citizens."

Authorities initially described the problem as a system malfunction when the sirens started blaring shortly before midnight Friday.

City spokeswoman Sana Syed said about 12:30 a.m. that Dallas Fire-Rescue crews were working to fix the problem.  But it took until about 1:20 a.m. to silence them for good because the emergency system had to be deactivated.

The system remains shut down Saturday while crews safeguard it from another hack. The city said the system should be restored Sunday or Monday -- in time for the thunderstorms that are expected to begin rolling through the area early next week.

One of the biggest challenges the security breach  posed was to the city's 911 call system, which has been strained recently by technical difficulties and short staffing.

Even as the city asked residents not to dial 911 to ask about the sirens, more than 4,400 calls were recived from 11:30 p.m. to 3 a.m. -- twice the average number made between 11 p.m. and 7 a.m, Syed said.

The largest surge  came from midnight to 12:15 as about 800 incoming calls caused wait times to jump to six minutes, far above the city's goal to answer 90 percent of the calls within 10 seconds.

"We understand that people were concerned," Syed said. "We had people asking if we were being attacked because of what's going on overseas."

Dallas officials said they have begun working with the Federal Emergency Management Agency to add an alert system that would send messages to all cellphones in the area when there is an emergency.

The city said it has also asked the Federal Communications Commission to help find who is responsible for the security breach.

In November, the City Council approved a $567,368 budget to maintain and repair all of the city's emergency sirens over the next six years.

Michigan-based West Shore Services was the winning bidder for the city contract.

The company's operations manager, Luke Miller, said Saturday that the city had not notified him the system had been hacked.

"I am trying to get information along with everyone else," he said. "I don't know know anything."

Miller said he expects his company will help investigate what went wrong.

City Council member Philip Kingston, a member of the Public Safety Committee, said Saturday morning that officials will move the compromised emergency system to the top of their agenda.

"And that's sad, because the list is so long," he said, referring to other problems, including the short-staffed 911 call center.

"If this is indeed hacking, it has just become top priority," Kingston said. "And you can put me down as terrified."

Jennifer Staubach Gates, who also serves on the Public Safety Committee and is chairwoman of the Budget, Finance and Audit Committee, said City Auditor Craig Kinton recently told her it was time for the city to review its security vulnerabilities.

"If it's hacking, it's extremely concerning," she said. "If someone's messing with our emergency system we've got an issue. We need to get to the bottom of it -- what kind of vulnerabilities do we have?"

Staff writer Eline de Bruijn contributed to this report.

(c)2017 The Dallas Morning News