A false emergency alert warning of a “radiological hazard” took over the television screens of some Jefferson County residents on Thursday night, sparking questions and concerns.

The false alarm was distributed to an unknown number of Wave cable customers and could have been the work of hackers who accessed the cable system, Jefferson County Emergency Operations officials told KING-TV.

The Emergency Operations Center sent a follow-up text alert that read, “This appears to have been an error, and is being investigated,” KING reported.

“So far it appears to only be happening in Jefferson County,” the Jefferson County 911 dispatch service posted to its Facebook page Thursday evening.

The Washington State Military Department’s Emergency Management Division is on the case, working with Jefferson County and the cable provider to “identify what went wrong, as well as to develop solutions to fill any security gaps,” said state military department communications director Karina Shagren. She said her department is also working with the State Emergency Communications Committee, which oversees Washington’s Emergency Alert System.