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What is the Signal messaging app and how secure is it?
Experts saying using even such a privacy-focussed platform for national security matters is very unusual.
The free messaging app Signal has made headlines after the White House confirmed it was used for a secret group chat between senior US officials. Signal has estimated 40-70 million monthly users - making it pretty tiny compared to the biggest messaging services, WhatsApp and Messenger, which count their customers in the billions. Data expert Caro Robson, who has worked with the US administration, said it was "very, very unusual" for high ranking security officials to communicate on a messaging platform like Signal.
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