Although Telegram was founded by a Russian, Pavel Durov (more on him later), the messaging app rejects any affiliation with Russia. Nonetheless, Alan Woodward, a cybersecurity expert who is a visiting professor at the University of Surrey, in England, said that “the fact that it’s not American” was a major attraction.

Mr. Woodward added that many users were suspicious that rivals like WhatsApp or Signal would allow backdoor access to Western intelligence agencies.

Before Telegram’s recent problems, institutions like the Kremlin and figures like Iran’s supreme leader, Ayatollah Ali Khamenei, had been among the messaging app’s 200 million users. But Telegram’s increasing popularity prompted scrutiny from countries like France, where investigators found that the app had become a platform for coordinating terrorism.

The growing criticism led Telegram to crack down on public channels used by the Islamic State. But the terrorist group has thwarted those efforts and continues to operate on the platform. (The channels are one of Telegram’s distinctive features, allowing messages to be broadcast to an indefinite number of users.) Mr. Durov and others at Telegram insisted that private messages would remain private.