|Original author(s)||Talmon Marco, Igor Magazinnik|
|Developer(s)||Rakuten Viber (part of Rakuten Inc.)|
|Initial release||December 2, 2010|
|Written in||C/C++/Python (desktop, using SIP and Qt frameworks), Objective-C (iOS), Java (Android)|
|Type||Instant messaging client, VoIP|
Viber is a cross-platform voice over IP (VoIP) and instant messaging (IM) software application operated by Japanese multinational company Rakuten, provided as a freeware for the Android, iOS, Microsoft Windows, macOS and Linux platforms. Users are registered and identified through a cellular telephone number, although the service is accessible on desktop platforms without needing mobile connectivity. In addition to instant messaging it allows users to exchange media such as images and videorecords, and also provides a paid international landline and mobile calling service called Viber Out. As of 2018, there are over a billion registered users on the network.
The software was developed in 2010 by Israel-based Viber Media, which was bought by Rakuten in 2014. Since 2017, its corporate name has been Rakuten Viber. It is based in Luxembourg. Viber's offices are located in Amsterdam, Barcelona, Brest, London, Manila, Minsk, Moscow, Paris, San Francisco, Singapore, Sofia, Tel Aviv, and Tokyo.
Viber Media might have been founded in Tel Aviv, Israel, in 2010 by Talmon Marco and Igor Magazinnik, who are friends from the Israel Defense Forces where they were chief information officers. Marco and Magazinnik are also co-founders of the P2P media and file-sharing client iMesh. The company was run from Israel, with much of its development outsourced to Belarus in order to lower labor-costs. It was registered in Cyprus. Sani Maroli and Ofer Smocha soon joined the company as well. Marco commented that Viber allows instant calling and synchronization with contacts because the ID is the user's cell number, unlike Skype which is modeled after a "buddy list" requiring registration and a password.
In its first two years of availability, Viber did not generate revenues. It began doing so in 2013, via user payments for Viber Out voice calling and the Viber graphical messaging "sticker store". The company was originally funded by individual investors, described by Marco as "friends and family". They invested $20 million in the company, which had 120 employees as of May 2013 .
On February 13, 2014, Rakuten announced they had acquired Viber Media for $900 million. The sale of Viber earned the Shabtai family (Benny, his brother Gilad, and Gilad's son Ofer) some $500 million from their 55.2% stake in the company. At that sale price, the founders each realized over 30 times return on their investments.
As of December 2016 According to Statista, there are 260 million monthly active users as of January 2019. The Viber messenger is mainly popular in Eastern Europe, Russia, the Middle East, and some Asian markets., Viber had 800 million registered users.
India was the largest market for Viber as of December 2014 with 33 million registered users, the fifth most popular instant messenger in the country. At the same time there were 30 million users in the United States, 28 million in Russia and 18 million in Brazil. Viber is particularly popular in Eastern Europe, being the most downloaded messaging app on Android in Belarus, Moldova and Ukraine as of 2016. It is also popular in Iraq, Libya and Nepal. As of 2018, Viber has over 70 percent penetration rate in the CIS and CEE regions, but only 15 percent in North America.
Viber is one of the more popular messenger applications in the top 5 social apps.  In January 2016, Viber surpassed WhatsApp in Russia, with about 50 million users. Viber was growing especially rapidly in urban areas like Moscow and St. Petersburg. In April 2016 the usage of Viber in Russia were twice higher than in 2015, it reached 66 million users. By 2018, Viber had reached 100 million users in Russia.  Another report from 2017 shows that Russian IM users prefer to use Viber or WhatsApp over other services. In Russia Viber plans to use the method of payment for shopping for goods and services.
Nikolay Nikiforov of the Federal Service for Supervision of Communications, Information Technology and Mass Media has declined to comment on the effect that law No 241-FZ (which has restricted use of some other encrypted chats such as Telegram) would have on Viber. 
Viber was initially launched for iPhone on December 2, 2010, in direct competition with Skype. It was launched on the Android platform on July 19, 2012, followed by BlackBerry and Windows Phone on May 8, 2012, and Nokia's Series 40, Symbian and Samsung's Bada platform on July 24, 2012, by which time the application had 90 million users.
In May 2013 with Viber 3.0, a desktop version for Windows and macOS was released. In August 2013, Viber for Linux was released as a public beta and in August 2014 a final version. In June 2016 a UWP-based desktop application for Windows 10 was released in the Windows Store. The desktop versions are tied with a user's registered Viber mobile number, but can operate independently afterwards. In 2015, a version for the iPad tablet and Apple Watch smartwatch was released.
Viber was originally launched as a VoIP application for voice calling. On March 31, 2011, Viber 2.0 was released which added instant messaging (IM) capabilities. In July 2012 group messaging and HD Voice engine were added to both Android and iOS applications.
In December 2012 Viber added 'stickers' to the application. In October 2013, Viber 4.0 was announced featuring a sticker 'market' where Viber would be selling stickers as a source of revenue. In addition, version 4.0 introduced push-to-talk capabilities, and Viber Out, a feature that provides users the option to call mobile and landline numbers via VoIP without the need for the application. Viber Out became temporarily free in the Philippines to help Typhoon Haiyan victims connect with their loved ones.
In November 2016, Viber version 6.5 launched Public Accounts to allow brands to engage in promotion and customer service on the platform, with initial partners including The Huffington Post, Yandex and The Weather Channel. The app integrates with CRM software and offers chatbot APIs for customer service. Viber Communities, an enhanced group chat feature, was introduced in February 2018.
Group calling was introduced with version 10 in February 2019.
On November 4, 2014, Viber scored 1 out of 7 points on the Electronic Frontier Foundation's "Secure Messaging Scorecard". Viber received a point for encryption during transit but lost points because communications were not encrypted with keys that the provider didn't have access to (i.e. the communications were not end-to-end encrypted), users could not verify contacts' identities, past messages were not secure if the encryption keys were stolen (i.e. the service did not provide forward secrecy), the code was not open to independent review (i.e. the code was not open-source), the security design was not properly documented, and there had not been a recent independent security audit. On November 14, 2014, the EFF changed Viber's score to 2 out of 7 after it had received an external security audit from Ernst & Young's Advanced Security Centre.
On April 19, 2016 with the announcement of Viber version 6.0, Rakuten added end-to-end encryption to their service, but only for one-to-one and group conversations in which all participants are using the latest Viber version for Android, iOS, Windows (Win32) or Windows 10 (UWP). The company said that the encryption protocol had only been audited internally, and promised to commission external audits "in the coming weeks". In May 2016, Viber published an overview of their encryption protocol, saying that it is a custom implementation that "uses the same concepts" as the Signal Protocol.
Viber's desktop version uses TCP and UDP ports 5242, 4244, 5243, 9785, and the standard HTTP/HTTPS ports 80 and 443.