Telegram is a cloud-based instant messaging and voice over IP service. Telegram client apps are available for Android, iOS, Windows Phone, Windows, macOS and Linux. Users can send messages and exchange photos, videos, stickers, audio and files of any type. Telegram's client-side code is open-source software but the source code for recent versions is not always immediately published, whereas its server-side code is closed-source and proprietary. The service also provides APIs to independent developers. As of April 2020, Telegram has 400 million monthly active users. The announcement included a promise to implement group video calls in 2020. The default messages and media use client-server encryption during transit. This data is also encrypted at rest, but can be accessed by Telegram developers, who hold the encryption keys. In addition Telegram provides end-to-end encrypted calls and optional "secret" chats between two online users on smartphone clients. However, the desktop clients (excluding macOS client) do not feature end-to-end encryption, nor is end-to-end encryption available for groups, supergroups, or channels. Telegram has defended the lack of ubiquitous end-to-end encryption by claiming the online-backups that do not use client-side encryption are "the most secure solution currently possible".
Development Telegram was launched in 2013 by the brothers Nikolai and Pavel Durov. Previously, the pair founded the Russian social network VK, which they left when it was taken over by the Mail.ru Group. Nikolai Durov created the MTProto protocol that is the basis for the messenger, while Pavel provided financial support and infrastructure through his Digital Fortress fund with partner Axel Neff joining as a second co-founder. The Company and the App was started in Russia and shifted to Germany. Telegram Messenger LLP states that its end goal is not to bring profit, but it is not currently structured as a non-profit organization. Telegram is registered as both an English LLP and an American LLC. It does not disclose where it rents offices or which legal entities it uses to rent them, citing the need to "shelter the team from unnecessary influence" and protect users from governmental data requests. Pavel Durov has said that the service was headquartered in Berlin, Germany, between 2014[31] and early 2015, but moved to different jurisdictions after failing to obtain residence permits for everyone on the team. Durov left Russia and is said to be moving from country to country with a small group of computer programmers consisting of 15 core members. According to press reports, Telegram had employees in St. Petersburg. The Telegram team is currently based in Dubai. Usage numbers In October 2013, Telegram had 100,000 daily active users. On 24 March 2014, Telegram announced that it had reached 35 million monthly users and 15 million daily active users. In October 2014, South Korean governmental surveillance plans drove many of its citizens to switch to Telegram. In December 2014, Telegram announced that it had 50 million active users, generating 1 billion daily messages, and that it had 1 million new users signing up on its service every week, traffic doubled in five months with 2 billion daily messages. In September 2015, an announcement stated that the app had 60 million active users and delivered 12 billion daily messages. In February 2016, Telegram announced that it had 100 million monthly active users, with 350,000 new users signing up every day, delivering 15 billion messages daily. In December 2017, Telegram reached 180 million monthly active users. In March 2018, Telegram reached 200 million monthly active users. On 14 March 2019, Pavel Durov claimed that "3 million new users signed up for Telegram within the last 24 hours." Durov did not specify what prompted this flood of new sign-ups, but the period matched a prolonged technical outage experienced by Facebook and its family of apps, including Instagram. On 24 April 2020 Telegram announced it had reached 400 million monthly active users. According to the U.S. Securities and Exchange Commission, the number of monthly Telegram users as of October 2019 is 300 million people worldwide.