The Dallas siren hack was carried out with radio signals

Dallas residents were awoken last weekend by the blaring of tornado sirens, but the weather was calm. It went on for more than an hour and a half, and at the end of it city officials admitted the system had been hacked. That conjures up a certain image of someone hunched over a computer gaining access to critical government networks. However, in an updated statement, city manager T.C. Broadnax says the “hack” wasn’t carried out with a computer, but via radio frequency.

The incident occurred just before midnight on Friday into Saturday, and went on until city officials threw up their hands in frustration and just unplugged the whole system. The local populace was understandably concerned, despite the apparently clear skies. Texas is prone to severe weather this time of year. In fact, three tornadoes touched down in the areas just a few days before the hack. The city first believed the incident to be a malfunction before later admitting that someone had accessed its control systems.

Broadnax was likely trying to put minds at ease with this update on the incident. He stressed that no city computer systems were infiltrated, and this was carried out entirely with radio frequencies. Is that really comforting, though? The city’s sirens, which were purchased just a decade ago, didn’t use encrypted signals. Broadnax didn’t share additional details on how the city’s sirens were activated, fearing someone else might figure out the method and set them off again.

Dallas is not alone in controlling its sirens with radio signals — it’s actually standard practice. The frequencies are public, and managed by the FCC. In 2004, the agency had to allocate a special block of spectrum after the increasingly powerful signals from wireless carriers started interfering with sirens. When the sirens need to be sounded, a signal is sent out from police dispatchers or weather monitors. Someone apparently figured out how to hijack that signal with their own transmitter. What if that’s possible elsewhere? There might be many other cities across the country using the same setup as Dallas.

Broadnax says Dallas has made changes to the system that should prevent anyone from using the same method to trigger the sirens. The system now relies on encrypted signals and other “safeguards.” This may just be a short-term fix as the city looks into replacing the sirens completely. And still, no one knows who set off the sirens in the first place, but an investigation is ongoing.

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