Poland’s railways have recently come under a form of electronic attack, as reported by Wired. The attack has widely been called a “cyber-attack” in the mainstream media, but the incident was altogether a more simple affair pursued via good old analog radio.

The attacks were simple in nature. As outlined in an EU technical document, Poland’s railways use a RADIOSTOP system based on analog radio signals at around 150 MHz. Transmitting a basic tone sequence will trigger any duly equipped trains receiving the signal to engage emergency braking. It’s implemented as part of the PKP radio system on the Polish railway network.

The attacks brought approximately 20 trains to a standstill, according to the BBC, with services restored within hours. There was no major safety risk in the event, something made clear in a statement from Polish rail authorities. Regardless, the attacks frustrated logistics across the rail network.

It’s believed the perpetrators of the attack were supporters of the Russian war effort, as the stop signals were also joined by broadcasts of the Russian national anthem and a speech from Russian President Vladimir Putin. The attacks have some significance to the invasion of Ukraine, as Poland has been a hub for crucial weapons deliveries supporting the defence of Ukraine.

The concern is that any unsophisticated individual could achieve the same results with cheap off-the-shelf equipment under $100. The emergency stop feature is completely insecure, which has been public knowledge for some time. Unlike an emergency brake on a passenger train, which requires proximity to actuate, the RADIOSTOP feature can be triggered at will from any remote location within transmission range. That makes catching perpetrators more difficult.

Poland’s railways will receive an upgrade to more secure cellular technology by 2025, with the 150 MHz system retained only for shunting duties and other edge cases. Interestingly, it will use GSM-R for connectivity, which is a big deal in Europe.

Until then, the vulnerability will remain as long as the 150MHz RADIOSTOP feature is enabled. Polish radio authorities may have their work cut out chasing down illegal transmitters in the meantime to prevent repeat attacks. It’s not the only way to bring a railway to a stop, but it’s unfortunately an easy and effective one.