Texas state officials are scrambling after 23 cities were hit with a “coordinated” ransomware attack.
The attack occurred Friday morning and the state’s Department of Information Resources says state and federal authorities are working with the towns to get their systems back online. As of 12:30 p.m. ET, a spokesperson for the state told Fortune he could not comment on the success of those efforts. An update is expected to be released later Monday afternoon.
Texas officials have also not yet listed the cities that were impacted by the attacks, though say “the majority … were smaller local governments.” The evidence, at the moment, points to a single attacker, though authorities say they are still in “response and recovery” mode.
State systems, they say, were not affected in the attack.
Ransomware is a malware tool that allows an attacker to lock up a computer system (or systems) until the owner pays a ransom demand. Last year, hackers shut down key systems across computers in Atlanta, stopping the city from processing payments or accessing courthouse information. And in 2017, officials in Mecklenburg county, N.C.—where the state’s largest city, Charlotte, is located—found itself in a similar situation. Officials in that area refused to pay the Bitcoin ransom.
Beyond officials in Texas, the investigation is being supported by the Department of Homeland Security, the FBI, FEMA and other federal entities.
More must-read stories from Fortune:
—FortuneChange the World 2019: See which companies made the list
—Q&A: Walmart CEO Doug McMillon on automation, the tragedy in El Paso, and more
—How the maker of the world’s bestselling drug keeps prices sky-high
—How the world’s biggest companies stay ahead
—Millennial workers are thriving in age-old workplaces
Subscribe to Fortune’s CEO Daily newsletter for the latest business news and analysis.