Telegram is a cross-platform messenger that allows you to exchange messages and media files in many formats  . A proprietary server part with closed source code is used , operating at the facilities of several companies in the USA and Germany, financed by Pavel Durov   in the amount of about 13 million US dollars annually  , and several open source clients, including those under licensed by the GNU GPL.
The number of monthly active users of the service, as of the end of March 2018, is more than 200 million people  . In August 2017, in his Telegram channel, Pavel Durov announced that the number of instant messenger users is increasing by more than 600 thousand daily  .
According to the research of Romir research holding in February 2018, on average, Telegram users in Russia spend 10-11 minutes a day on it. The largest share of users falls on Russians aged 18-24 years. Telegram in Moscow is twice as popular as in other cities of Russia as a whole, especially among an audience of 35 to 44 years old  .
In addition to the standard messaging in dialogs and groups, in the messenger you can store an unlimited number of files ( → ), keep channels (microblogs) ( → ), create and use bots ( → ).
Starting April 16, 2018, restrictions on the use of the messenger in Russia have been imposed
The project was created by Pavel Durov , founder of the VKontakte social network . In an interview with The New York Times, Pavel said  that the initial idea of the application came to him back in 2011, when special forces came to his door . When the latter nevertheless left, Durov immediately wrote to his brother Nikolai. Then he realized that he did not have a safe way to communicate with his brother. The service is based on the MTProto correspondence encryption technology developed by Paul’s brother – Nikolai   . Telegram itself was originally an experiment owned by Pavel Digital Fortress in order to test MTProto under heavy loads .
On August 14, 2013, the first Telegram client for iOS devices was introduced  .
On August 22, 2013, one of the participants in the Durov’s Android Challenge contest wrote and made publicly available the first application for the Android operating system that is compatible with Telegram (uses the same MTProto protocol)  .
In October, the project opened a website and presented the official version of Telegram for Android with open source code (GPL2)   . A previous version of the program is available under the name “Unofficial Telegram S”  .
On November 7, 2013, third-party service clients for Windows and macOS with limited functionality appeared. The concept of a web version of the client was also developed  .
In November, the program had, according to TJournal, about 1 million installations  .
In January 2014, an unofficial web version of Webogram  was released from a former VKdeveloper Igor Zhukov.
On July 21, 2014, the Telegram HD app for iPhone and iPad appeared on the App Store , which was downloaded by Telegram Messenger LLP  .
The new application received a special version for the Apple iPad , improved support for high-resolution video and photos, and added the ability to send animated images in gif format . On the official website of the messenger, this application is indicated as the client for iOS.
On October 15, 2014, Telegram added support for aliases by which it is possible to communicate with users without even knowing their phone number, and also launched a web client  .
On January 2, 2015, support for stickers was added to Telegram . Initially, there are 14 stickers in the application, but any user can modify them or add their own. Unlike many applications, Telegram stickers are completely free  .
In February 2016, one of the creators of Telegram Pavel Durov said that more than 100 million people are using the messenger, while the service delivers about 15 billion messages daily. Back in September 2015, Telegram transmitted 12 billion messages per day  .
In April 2016, it became known that in May 2015, Google was considering buying a messenger for more than 1 billion US dollars   .
In May 2016, it became possible to edit sent messages. It is possible to make changes within two days from the moment of sending. In this case, a special label  will appear in the message .
On November 22, 2016, the developers launched the Telegraph project – a blog platform, a free publishing tool that allows you to create publications, reviews, insert photos and all kinds of embedded code. Telegraph is a hybrid of a blogging platform, messenger and platisher (similar to Medium ), with the concept of anonymous imageboards .
On January 3, 2017, one of the developers added the ability to delete his sent messages  . After the sender has deleted the message, the interlocutor will not be able to see the deleted message.
In March 2017, V. D. Solovey , citing an anonymous source, said that Russian intelligence agencies had access to user messages and their archive for three years. Pavel Durov called this statement a duck  .
On May 15, 2017, it became known that the desktop version of Telegram was able to make calls  .
On May 16, 2017, the Telegram administration announced that it would not provide information to Russian government agencies  .
On May 19, 2017, along with the new Telegram update for iOS, embedded HTML5 games were removed . According to the founder of the messenger Pavel Durov , representatives of the App Store did not approve of the publication of a new version of the messenger with built-in games, threatening the Telegram team with deleting the application from the store  .
On June 28, 2017, Roskomnadzor entered the program in the “Register of Information Distributors”  .
On September 27, 2017, Durov announced the FSB ’s request on July 14 to provide “information necessary for decoding received, transmitted, delivered and (or) processed electronic messages”, as well as the subsequent drafting of an administrative protocol for failure to comply with this requirement  .
On October 11, 2017, an updated version of the Telegram messenger for iOS and Android in Russian appeared, prepared using the new platform translations.telegram.org, with the help of which the messenger interface was translated into Ukrainian, French, Malay and other languages. The appearance of the media player has also changed, and it has become possible to share your geo-location  .
An example of the attitude of the Russian security agencies towards the messenger is the following fact: on October 16, 2017, the Meshchansky District Court of Moscow fined Telegram 800 thousand rubles for refusing to provide the FSB with information for decoding messages regarding 6 numbers that use this messenger  . Commenting on the situation, Pavel Durov stated that he considers the FSB requirements on Telegram to be contrary to the Constitution of the Russian Federation, and asked lawyers who want to tackle the issue to contact him.
In November 2017, the Telegram channel was first blocked due to audio piracy  .
On March 20, 2018, the Supreme Court of Russia upheld the FSB’s requirement to provide keys for decrypting Telegram correspondence  . On the same day, Roskomnadzor notified Telegram of the need to comply with the requirements of the law on the provision of information to the FSB of Russia. If Telegram does not provide the FSB encryption keys within 15 days, it may be blocked in Russia  . The creator of the messenger announced his refusal to give the FSB encryption keys for correspondence in Telegram  .
March 29, 2018 there was a failure in the messenger. The problem affected both the application and the web client. According to company representatives, the problem affected residents of Europe, the Middle East and the CIS. Users have lost the ability to exchange messages, make notes in group chats and channels, and also make calls. According to Pavel Durov, the reason is a power outage in one of the data centers. According to Kommersant , the backup channels probably did not work due to errors in the system configuration  .
On July 26, 2018, the messenger launched Telegram Passport  . This service can store personal data – passports, passports, receipts, utility bills, and other documents. They can be downloaded once into the Telegram cloud storage, protected by end-to-end encryption, and then shared with services requiring authorization. Previously, these documents had to be downloaded again each time  . The messenger itself will not have access to this data  .
On August 28, 2018, the messenger’s lawyer Pavel Chikov said that Telegram agreed to transmit to the special services the IP addresses and phone numbers of users suspected of terrorism on the basis of a court decision  .
“Threats to block Telegram, if we do not give out the private data of users, will lead to nothing. Telegram protects freedom and privacy. ” – Pavel Durov
On March 24, 2019, Telegram provided the ability to completely delete messages from itself and the interlocutor, regardless of the statute of limitations.Telegram announced that the messenger reached 35 million users per month and 15 million active users  . In October 2014, South Korean government plans to monitor messengers forced many citizens to switch to Telegram  . In December 2014, Telegram announced that the messenger has 50 million active users generating 1 billion daily messages, and that 1,000,000 users are logged in to the messenger every week  . In September 2015, it was announced that the application has 60 million active users and delivers 12 billion daily Messages . In February 2017, Telegram announced that the messenger reached 100 million active users, with 350,000 new users registering daily and 15 billion messages sent  , and in March 2018, the Telegram audience grew to 200 million active users  .
In October 2018, the daily Russian audience of the Telegram mobile application amounted to almost 3.4 million people aged 12-64 years living in cities with a population of 100 thousand or more (100+). According to the research company Mediascope, the monthly Russian audience of the Telegram mobile application in October 2018 approached 9.3 million people.For the messenger, the MTProto protocol was created , which involves the use of several encryption protocols. For authorization and authentication, RSA-2048 and DH -2048 algorithms are used for encryption  ; when transmitting protocol messages to the network, they are encrypted with AES with a key known to the client and server. With the transition to the MTProto 2.0 protocol , the SHA-256 cryptographic hash algorithm is used . 
On October 8, 2013, the mode of “secret” chats (Secret Chats) appeared in the messenger . This mode realizes encryption, in which only the sender and receiver have shared key (end-to-end encryption) using the AES-256 algorithm mode IGE ( Engl. Infinite Extension Garble) for forwarded messages  . Unlike normal mode, messages in secret chats are not decrypted by the server, the correspondence history is saved only on those two devices on which the chat was created.
When exchanging files, you can either send files from the device or search for media content on the Internet, if you are using a mobile version for iOS or Android. The size of the transferred files is limited to 1.5 GB  . The program uses a system to resume files after disconnection  .
It is possible to change the formatting of the text, making it: bold , italics.
In 2018, version 4.8 for Android introduced innovations: watching videos in parallel with downloading files and an automatic night theme that turns on at a later time of the day, in low light or when the battery charge is less than 25% .