A man holds a laptop computer as cyber code is projected on him in this illustration picture created on May 13, 2017. REUTERS/Kacper Pempel/Illustration

By Raphael Satter and AJ Vicens

WASHINGTON (Reuters) -Hackers are hijacking U.S. radio transmission equipment to broadcast bogus emergency messages and obscene language, the Federal Communications Commission said on Wednesday.

In a public notice, the FCC said a "recent string of cyber intrusions against various radio broadcasters" had occurred, resulting in the issuance of the U.S. Emergency Alert System's "Attention Signal." The signal is an attention-grabbing sound that is meant to precede official announcements related to tornadoes, hurricanes, earthquakes and other emergencies.

The FCC said the hackers appeared to have compromised improperly secured equipment made by the Swiss network audio company Barix and reconfigured it "to receive attacker-controlled audio in lieu of station programming." The agency said affected stations "broadcast to the public an attacker-inserted audio stream that includes an actual or simulated Attention Signal and EAS alert tones, as well as obscene language, and other inappropriate material."

The FCC notice cited reporting from the last few days about radio streams in Texas and Virginia being hijacked to broadcast bigoted or offensive material. The agency urged broadcasters to take basic security precautions, such as changing default passwords and regularly installing updates.

Barix did not immediately respond to an email seeking comment. However, in a 2016 statement issued in the wake of a similar spate of hijackings, the company said: "Barix would like to emphasize that its devices are secure for Broadcast use when set up correctly and protected with a strong password."

(Reporting by Raphael Satter in Washington and AJ Vicens in Detroit; Editing by Matthew Lewis)