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SpaceX boss Elon Musk believes there is a high chance that his Starlink satellite broadband service could be targeted by Russia.
Ukraine confirmed on Monday that it had received a donation of satellite internet terminals after its appeal to Mr Musk for help in keeping online communications working after the Russian invasion last week.
The vice-prime minister of Ukraine, Mykhailo Fedorov, tweeted a photo of a lorry carrying Starlink equipment, but security researchers said that they could potentially be tracked and targeted by Russian military.
After some of the concerns came to light, Mr Musk said that the system should be used with caution.
“Important warning: Starlink is the only non-Russian communications system still working in some parts of Ukraine, so probability of being targeted is high,” he tweeted.
It was not immediately clear how many units have been sent to Ukraine after Mr Fedorov on Saturday first made his appeal to the SpaceX boss for the units.
But Mr Fedorov tweeted a photo of a unit apparently in position on Wednesday and said that the system was keeping “our cities connected and emergency services saving lives”.
Starlink uses a system of more than 2,000 satellites in low-Earth orbit to supply the internet in areas where connectivity is difficult or unavailable owing to natural disasters or war. It requires a small roof-based receiver with a clear view of the skies to receive signals from the satellite.
John Scott-Railton, a senior researcher at the University of Toronto who has studied surveillance in conflict zones, said on Twitter that the terminals could potentially send enough of a signal to be identified and targeted.
He said that Russia had decades of experience hitting people by monitoring their satellite communications, including the killing of Chechen separatist leader Dzhokhar Dudayev in 1996 while he was reportedly making a satellite phone call.
Mr Scott-Railton said the systems were different but that it was not clear if the Starlink technology had vulnerabilities because it was so new.
He wrote on Twitter that satellite internet felt like a saviour for the Ukrainians but could quickly introduce “deadly new vulnerabilities.”
He said: “If you don't understand them, people die needlessly until they learn and adapt.”
Mr Musk responded to the concerns by advising users to turn on Starlink only when it was needed and to place the receivers as far from people as possible.
Mr Musk said the software for the system had been updated so the system could be powered from a car cigarette lighter and provide a signal on the move.
Most parts of Ukraine still have the internet, but in the event of a complete shutdown experts said the Starlink system could provide hot spots for communication.