Police said Thursday they had arrested more than 800 people across Europe after shutting down an encrypted phone network used by organised crime groups to plot murders and drug deals.
French and Dutch police said they hacked into the EncroChat network so they could read millions of messages "over the shoulders" of suspects as they communicated with custom-made devices.
Britain said it had arrested 746 people as a result of the operation in what it called a "massive breakthrough" against organised crime, while there were also arrests in countries including Norway, Spain, and Sweden.
EncroChat sent a message to its estimated 60,000 users in June warning them to throw away their 1,000-euro devices as its servers had been "seized illegally by government entities". It has now been shut down.
The hack allowed police "an unprecedented look into the heart" of organised crime groups, Wil van Gemert, Deputy Executive Director of the EU police agency Europol, told a press conference in The Hague.
Police then foiled crimes including "violent attacks, corruption, attempted murders and large-scale drug transports," Europol and the EU judicial agency Eurojust added in a joint statement.
"Certain messages indicated plans to commit imminent violent crimes and triggered immediate action."
- 'So worrying' -
Some of the encrypted messages "were so worrying that it went far beyond our imagination," said Jannine van den Berg, Chief Constable of the Dutch police's central unit.
"It was as if though we were sitting at the table where criminals were chatting," she told the press conference.
French authorities launched the investigation in 2017 after finding that EncroChat phones were "regularly" found in operations against criminal groups and that the company was operating from servers in France.
They then "put a technical device in place to go beyond the encryption technique and have access to the users' correspondence," the statement said.
Between 90 and 100 percent of EncroChat clients were linked to organised crime, according judicial sources, with between 50,000 to 60,000 of the phones in circulation.
Dutch police then became involved based on information shared by French police.
A joint Dutch-Franco investigation team unearthed a "colossal number of encrypted data," Carole Etienne, the public prosecutor for the French city of Lille, told AFP.
Law officials were then able to "intercept, share and analyse millions of messages that were exchanged between criminals to plan serious crimes" later shared with police including in Britain, Sweden and Norway.
- 'Power off' -
"We've been able to see what's happening in real time with these criminals," Andy Kraag, head of Dutch police's central investigations division told the press conference.
Dutch police had busted 19 meth labs, seized 10 tonnes of cocaine and thousands of kilos of crystal meth and arrested more than 100 people, Kraag said.
In Britain, police arrested 746 suspects, recovered more than 54 million pounds (59.8 million euros, $67.5 million) as well as 77 guns including an AK-47 assault rifle and 1,800 rounds of ammunition.
"This is the broadest and deepest ever UK operation into serious organised crime," Britain's National Crime Agency director of investigations Nikki Holland said in a statement.
The French and Dutch authorities said the decision to hack into the encrypted phone network was justified.
"The platform targeted in this operation catered specifically to the needs of criminals," said Europol's Van Gemert.
EncroChat sent what it called an "emergency" text to its users on June 13 saying it had been compromised.
"Today we had our domain seized by government entities," said the message. "You are advised to power off and physically dispose your device immediately."AFP