Law enforcement agencies across Europe are celebrating their infiltration of an encrypted messaging service used by organised criminal networks, resulting in 746 arrests, $97m in cash and more than two tonnes of drugs seized.

Earlier this year, French and Dutch authorities succeeded in hacking Encrochat – a subscription service that sold phones designed for full user anonymity.

The devices, sold for around $2,400, contained an encrypted interface that was hidden in a second operating system so as to not arouse suspicions.

Functions like camera, microphones, and GPS were removed from the phones, and it was fitted with features to easily erase data.

For months, police had been silently watching as Encrochat users made dealings on devices they believed were cryptographically secure.

In June, Encrochat got wind of the cyber operation and shut down its servers.

“Due to the level of sophistication of the attack and the malware code, we can no longer guarantee the security of your device,” Encrochat told its users in a message.

More than two tonnes of Class A and B drugs were seized. Image: Supplied/NCA

“We took immediate action on our network by disabling connectivity to combat the attack.

“You are advises [sic] to power off and physically dispose your device immediately.”

For many users, Encrochat pulled the plug far too late.

Data had long been pooled and combed through by authorities who had already begun making arrests and dismantling the criminal organisations who were operating through Encrochat.

On Friday morning, the UK’s National Crime Agency (NCA) announced that it had made over 700 arrests and seized $97 million in cash and two tonnes of drugs thanks to the hacking operation.

More than 28 million Etizolam pills were seized. Image: Supplied/NCA

NCA’s Director of Investigations, Nikki Holland, said the Encrochat breach was “like having an inside person in every top organised crime group in the country”.

“Together we’ve protected the public by arresting middle-tier criminals and the kingpins, the so-called iconic untouchables who have evaded law enforcement for years, and now we have the evidence to prosecute them,” Holland said.

“I’d say to any criminal who uses an encrypted phone, you should be very, very worried.”

In the Netherlands – where Encrochat was based – the breach has so far led to authorities seizing 8 tonnes of cocaine and 1,200 kg of crystal meth.

An anonymous source told Motherboard that Encrochat’s users “are fucked”, adding that people had been “[talking] about murder, buying kilos, buying guns” on devices they thought would give them impunity.