The popular messaging app Telegram risks being blocked in Russia after refusing demands to hand over its encryption keys to give the FSB security service access to users' data. Here are four things to know about the company, which says it has 200 million active users:
WHIZZ-KID BILLIONAIRE
Known as Russia's Mark Zuckerberg after the Facebook boss, Pavel Durov has amassed a fortune of $1.7 billion (1.4 billion euros) at 33, according to Forbes magazine. He founded popular social networking site VKontakte in 2006 and Telegram - with his brother Nikolai - in 2013. Unlike his sibling, Pavel doesn't shy away from the limelight.
He once threw bank notes from his office window in Saint Petersburg, shows off his sculpted chest on Instagram, and has quarrelled with shareholders and the authorities. Durov left Russia in 2014 after refusing to hand Russian authorities personal data of pro-European Ukrainian activists. He later settled in Dubai.
STRICTLY CONFIDENTIAL
Telegram boasts that it keeps users' personal data confidential and champions internet freedoms. "Unlike other popular apps, Telegram doesn't have shareholders or advertisers to report to," Pavel Durov wrote on Telegram's blog last month. "We haven't disclosed a single byte of our users' private data to third parties," he added.
Durov offered whistleblower Edward Snowden a job after his revelations of mass surveillance.
THREAT OF TERRORISM
The service has been accused of aiding terror plotters by refusing to share users' information. Iran recently restricted its use. After the Paris attacks in 2015, Telegram shut accounts linked to the Islamic State group and has blocked 6,000 others.
Durov has said Telegram draws a clear line, with no restrictions on "criticising local authorities, challenging the status quo and engaging in political debate." On the other hand, "promoting violence and calling for actions that can harm innocent people are not OK," he wrote last year.
LURING INVESTORS
Investors are closely watching Telegram's move into cryptocurrency. Experts say the messenger wants to create its own virtual currency. The messaging service has raised $1.7 billion this year alone, a record figure for the sector, to develop the blockchain technology on which cryptocurrencies are based. But the service's heady growth has also had glitches. Last month the system went down for a few hours in Europe and the Middle East. "Every service growing too fast is bound to experience growing pains, unfortunately," Pavel Durov said. "Telegram is no exception, although we strive to be one."