This hack is clearly an invocation of the Emergency Alert System. The EAS is a hierarchically-organized digital message propagation system that has no authentication scheme for the vast majority of the nodes that participate in the network. Since every moderately-sized licensed broadcast radio and TV station in the United States is required to participate in the network, that is a lot of attackable nodes.
The hierarchy is easy to exploit if you wish to spoof an alert on a specific station. All you need to know is the specific list of stations that your target listens to for alerts and a mobile radio transmitter that you can position relatively closely to your target's EAS receiving equipment. The list of "source" stations for your target is often public information, or can be deduced very easily. (Search for "<city> eas plan" in your favorite search engine.) The radio transmitter required is nothing more than a VHF two-way radio, which can often be a "modded" Amateur Radio which can transmit outside of the legal Amateur bands.
- Step 1: Assemble an EAS alert on a computer using a little bit of code to generate the appropriate tones and an audio editor to stitch them together. The exact format is tricky, but the information is publicly available.
- Step 2: Find your likely target's listening list. These are often listed as the "Local Primary" and "Local Secondary" stations in your target's metropolitan area. These, unfortunately, are hard to spoof because broadcast-band FM and AM transceivers are harder to get a hold of. Instead, look up the NOAA weather radio transmission frequencies in your target's area. These stations are often used as additional EAS sources by almost every broadcast station in the system, and they are easy to spoof with portable equipment.
- Step 3: Put the spoof transmitter in a car and drive as close as possible to the target's published studio headquarters. Targets often place their receiving equipment in their primary studio locations.
- Step 4: Put your transmitter into transmit mode and play back your spoofed alert. You need to remain nearby just long enough to complete the injection process. With a short message you only need about 60 seconds.
- Step 5: Drive away. The automated relay system at your target will do the rest.
Step 4 (transmission) is extremely easy, even with low-powered equipment (250mW). Because of your proximity and the FM Capture Effect you will have no problem overpowering the real source station without adversely affecting or alerting anyone outside a 1/2 mile radius.
My guess is the attackers here did precisely this. They probably exploited this TV station by spoofing a local NOAA weather radio channel that the TV station was listening to for alerts.