Protesters hold signs in front of police officers a day after a large demonstration against an extradition law in Hong Kong. (EDWIN KWOK/EPA-EFE/REX)

Telegram, the encrypted messaging platform, reported a massive cyberattack stemming “mostly from China” while the app was widely used by demonstrators in Hong Kong.

The company said it was hit by a powerful distributed denial of service (DDoS) attack, which filled servers with junk requests. In a series of tweets, Telegram said its servers were inundated with scores of “garbage requests” that interrupted users’ connections and kept the servers from processing “legitimate requests.” The junk requests did not threaten users’ data, the company said.

Pavel Durov, Telegram’s chief executive, said the cyberattack was traced to “IP addresses coming mostly from China” and that it “coincided in time with protests in Hong Kong.” The app, which says it has 200 million users worldwide, has been widely used in Hong Kong to coordinate demonstrations against a controversial extradition bill. Earlier this week, Hong Kong police arrested Ivan Ip, who ran a Telegram messaging group with thousands of members. Officials charged Ip with conspiracy to commit public nuisance, according to the Hong Kong-based South China Morning Post newspaper.

Hong Kong’s protests ignited over a bill that would allow extraditions to mainland China. A reading on the extradition bill was postponed by lawmakers for a second time on Thursday. Demonstrations had shut down central areas of the city and triggered a violent response from riot police.

The Post’s Shibani Mahtani reports that the city largely returned to normal Thursday morning after demonstrators cleared out late Wednesday. Still, tear gas canisters and rubber bullets littering the streets offered quick reminders of this week’s unrest. Hong Kong police were not able to give a specific number of people arrested during Wednesday’s demonstrations. Local outlets reported that injured demonstrators were being questioned by police once they arrived at area hospitals.

Telegram has been employed for widespread protests before — and has faced government crackdowns. Last year, Durov said the app would fight Russia’s attempts to ban the platform over data privacy issues. In April 2018, a court in Moscow banned Telegram after the company would not provide encryption keys to a Russian security agency.

Iran also called on Telegram to block “terrorist channels” during protests in January 2018. An Iranian government minister said that if Telegram did not comply, the government would block the app. During anti-government protests throughout Iran, Telegram removed at least one channel that called for violence. But at the time, Durov said he would not shut down other channels e deemed peaceful.