It's been downloaded more than one billion times and has taken centre stage in battling the Russian disinformation campaign over Ukraine, but what exactly is Telegram and why is it so essential to the war?
What is Telegram?
It's similar to WhatsApp - and Twitter. The interface echoes WhatsApp's chat layout but Telegram users can access groups beyond those set up by their own contacts. And while anyone following an account on Twitter would have to monitor that feed, or rely on the app's algorithm to flag its tweets, Telegram posts alerts whenever new information has been added to a chat, in the same way WhatsApp users receive chat notifications.
Why are Russians flocking to it?
Russia heavily censors internet content to prevent its citizens from seeing critical reports of its actions. Russian president Vladimir Putin tightened controls even further this month by banning access to foreign news outlets including BBC, Voice of America and Deutsche Welle. Putin has also blocked Russians from accessing Facebook, Twitter and Instagram, seeking to have Meta recognised as an "extremist organisation".
Russia also passed a law this month that makes reporting what the state deems as "fake news" punishable with up to 15 years in prison. The Kremlin insists invading Ukraine be described as an essential "special military operation" and news outlets that don't comply are considered to be reporting "fake news".
As the Russian president continues to crackdown on access to information outside state media, its people are seeking ways around these tight controls with Telegram.
Who is Telegram's owner Pavel Durov?
Born in Russia, Telegram's founder and owner Pavel Durov was once celebrated as his home country's answer to Mark Zuckerberg, thanks to his hugely popular VKontakte (VK) social network. That changed when Durov refused to block opposition groups on the network and police carried out searches on his home and offices.
VK began to fall under the control of Russian authorities and Durov set up Telegram in 2013. Durov refused to hand over Ukrainian users' data to the Kremlin following Russia's invasion and seizure of Crimea in 2014 and he fled the country. The 37-year-old billionaire and self-described libertarian is now a citizen of two-island nation St. Kitts and Nevis, in the Eastern Caribbean.
Last week Durov emphasised his commitment to the privacy of the app's Ukrainian users.
Why has Telegram not been shut down in Russia?
Russia's attempts to prevent its citizens from accessing Telegram have failed. It banned the app in 2018 after Durov refused the Kremlin access to users' messages. However, Durov found a way to route traffic through other websites and Russian regulators couldn't stop people inside the country from accessing the app. In 2020, Russia conceded and reversed its unenforceable ban.
Who uses Telegram?
It's hugely popular in Russia and Eastern Europe, where more groups than individuals have verified accounts.
Telegram says it has been downloaded one billion times and has an active global user base of around 500 million.
Ukrainian President Volodymyr Zelenskyy uses the platform daily to broadcast what's happening in Ukraine from his verified account. Zelenskyy shares nightly video addresses from his Kyiv office to 1.5 million subscribers, as well as video and text updates on the situation across Ukraine throughout the day.
Why is it controversial?
Up to 200,000 users can be in one group chat and remain anonymous, while channels can post information to an unlimited number of subscribers. To this end, the app has attracted a large base of extremist organisations.
It has also come under scrutiny for requiring users to opt-in to its end-to-end encryption feature - the most secure method of transferring data between devices - rather than making it a default policy.
The app has taken steps to removing extremist groups and says that moderators constantly monitor reports on the app.