Russian activists from a group called the Anti-Corruption Foundation want to sue MTS because they believe the operator helped hack into their accounts on messaging app Telegram, the Financial Times reported.
They published documents they claim show that Russia’s largest operator helped unidentified intruders gain access to their Telegram accounts.
Russian law gives the FSB the right to access any user data, but with the approval of a judge.
Pavel Durov, the founder and chief executive of Telegram, suspects Russia’s secret service was behind the hacks.
“This is technically possible everywhere, but democratic countries typically try to avoid intercepting SMS without a court order, because such measures are highly visible and can lead to public uproar,” he said.
The leader of the anti-corruption group, Alexei Navalny, is looking into a US class-action lawsuit after activists Oleg Kozlovsky and Georgy Alburov received notifications that their Telegram accounts had been accessed from other devices last month. MTS is listed on the NYSE.
Their phone records show that MTS turned off their text messaging services in the early hours of 29 April after which someone using Tor, an anonymous web browser, gained access to their accounts by requesting confirmation codes to an unknown number. Their text services were restored later that morning after the hack.
They admit they did not make use of Telegram’s two-factor authentication or secret chat feature but blame MTS for helping the hacker.
“You can’t blame someone for having their car stolen if they leave it outside rather than in a garage,” Kozlovsky said.
The hack has raised concerns over how secure Telegram is, which is popular because of its privacy settings.
MTS denies the charges and said it will conduct an audit to check if the incident was due to a virus attack.
Earlier this week, WhatsApp was temporarily blocked in Brazil because a judge said the messaging app firm was not handing over information in a criminal investigation.
In the US, the FBI and Apple are involved in an ongoing tussle over unlocking iPhone encryption data.