The instant messaging app Telegram, created by Russian Internet guru Pavel Durov, says it has blocked dozens of accounts associated with the jihadist Islamic State group.
The move came as pressure builds on new instant messaging services like Telegram as they balance their obligations to users against security concerns following the deadly attacks in Paris and the recent downing of a Russian plane in Egypt.
Telegram, a free app which was launched in 2013, says it "provides a secure means of communications everywhere on the planet" and blasts Internet giants Facebook and Google on its website for giving private data to third parties.
It offers an encrypted chat service with self-destructing messages and has recently launched a way to create public channels to broadcast to unlimited audiences.
According to the Middle East Media Research Institute (MEMRI), the technology is fast becoming popular among jihadi groups, with ISIS and Al-Qaeda groups creating several channels.
"We were disturbed to learn that Telegram's public channels were being used by ISIS to spread their propaganda," the service said on its own Twitter account late Wednesday.
"As a result, this week alone we blocked 78 ISIS-related channels across 12 languages," it added.
Telegram said it identifies offensive public content by reviewing user reports.
"We were able to identify and block these public ISIS channels thanks to your reports," it said.
Telegram's Durov specified that the "only publicly available channels could be reported and blocked" and denied that he can intercept conversations.
Encryption of communications surged after fugitive ex-NSA employee Edward Snowden revealed in 2013 the massive data harvesting done by US agencies.
Telegram quickly amassed a following. While the precise number of users is unknown, in August the company said it is used to send 10 billion messages every day.
In the aftermath of the attacks however it could become harder for Telegram to defend its policy, as governments are likely to push for restrictions on the technology so it can better carry out surveillance of extremist groups.
Britain earlier this month published draft legislation that would give security officials access to Internet communication records of suspects.
CIA Director John Brennan complained Monday that some technologies -- without specifically mentioning encryption -- "make it exceptionally difficult, both technically as well as legally, for intelligence and security services to have the insight they need to uncover" terror plots.
Telegram has been targeted in Iran, and there are calls to ban it in Russia.
Durov previously admitted that ISIS jihadists use his network but stood by his policy to keep conversations private.
"I think that privacy, and our right for privacy, is more important than our fear of bad things happening, like terrorism," he said at a conference organized by TechCrunch in late September.
"Ultimately, ISIS will always find a way to communicate among themselves," Durov said when asked how he sleeps at night knowing ISIS uses his product.
Durov, the enfant terrible of Russia's Internet industry together with his brother Nikolai, developed the popular Vkontakte social networking site, a Russian version of Facebook.
He made waves in 2014 when he disclosed Russia's FSB security service had demanded he turn over personal data of Ukrainian protest groups that had toppled a pro-Moscow leader. He said that to obey would have been a betrayal of the trust of users.
But he ultimately lost control of VKontakte and left the country two years ago to focus on Telegram, based in Berlin.
More recently he appeared to also thumb his nose at US intelligence, writing on Facebook that "the (National Security Agency) tried to secretly recruit some of Telegram developers" and deriding "such invasive activities".
Earlier this week he wrote on Facebook that he mourned the Paris attacks that took place "in the most beautiful city in the world," but also criticized the French government.
"I think the French government is as responsible as ISIS for this, because it is their policies and carelessness which eventually led to the tragedy.
"They take money away from hardworking people of France with outrageously high taxes and spend them on waging useless wars in the Middle East and on creating parasitic social paradise for North African immigrants."