Last week, around 2:30 a.m., blaring emergency sirens woke the people of two Texas towns… and then, until about 4:00 a.m., the alarms kept sounding, on and off, until crews finally managed to turn them off.

The towns of DeSoto and Lancaster are both in Tornado Alley: one of two regions of the US that have a disproportionately high frequency of tornadoes (the other being Florida). The outdoor alerts are meant to warn people to get to safety. But there were no tornados on 12 March: just the noise of false alarms that had been set off by hackers, as officials of the two towns concluded.

Over 30 sirens kept going on and off, with 10 in DeSoto and 20 in Lancaster.

The city of DeSoto said in a statement that there was no malfunction in the warning system. The false alarms set off in both cities seem to have been triggered intentionally. The matter’s been turned over to the affected cities’ police departments for investigation.

City residents took to Twitter to try to figure out what was going on:

Lancaster officials warned that whoever’s responsible is looking at arrest and prosecution:

Based on the widespread impact to the outdoor sirens located in two separate cities, including Lancaster, it has become evident that a person or persons with hostile intent deliberately targeted our combined outdoor warning siren network.

Sabotage against a public warning system is more than vandalism. It is a criminal act and those responsible are subject to arrest and prosecution.

The cities managed to take the hacked systems offline the next morning, and as of Monday this week, they were still offline.