In the hours after the deadly terror attack on Monday in Manchester there was a flurry of activity on the Islamic State militant group's favorite app, an encrypted messaging service called Telegram. Even before authorities released details on the attack, ISIS supporters flooded the app's private and public channels with celebratory messages.
Telegram has become one of ISIS's primary means for disseminating information and bringing together supporters. Following Monday's bombing, it was a hub for pro-ISIS propaganda and ultimately a source for the group's official claim of responsibility.
As social media platforms such as Twitter and Facebook increased their efforts in recent years to shut down pro-ISIS accounts, Telegram has filled the void. Since around 2015, analysts say there has been an exodus of extremists to the app in search of better privacy and the freedom from being shut down by moderators.
"We've seen a clear trend of growing use of Telegram by almost all terror groups all over the world," Gabriel Weimann, a professor at the University of Haifa in Israel and author on online extremism, told HuffPost.
The rise of Telegram as a part of ISIS and other terrorist groups' communication strategy in recent years has shown how extremists adapt to technology in the face of attempts to shut down their online presence. ISIS has long used social media platforms to spread its propaganda and recruit followers, and Weimann explains that in general terror groups are early adopters of new online platforms and services they can exploit.
Telegram works much like the Facebook-owned WhatsApp, using end-to-end encryption to protect shared information. The company claims to have over 100 million users, and offers features like self-destructing messages to ensure greater privacy. Users can communicate either directly, in private groups or on channels.
The app was originally started in 2013 as a means of providing a more secure messaging service, with its creator Pavel Durov stating that the app was intended to prevent Russian security services from accessing communications between users.
Durov is a kind of Russian equivalent of Mark Zuckerberg, coming to prominence in 2006 after he founded VKontakte ― a social media platform more popular than Facebook in Russia. As the Kremlin cracked down on internet freedoms and put pressure on Durov, he decided to flee the country in 2014 and sell his stake in the company for what is estimated to be hundreds of millions of dollars.
Durov is now a citizen of the Caribbean island nation of St. Kitts and Nevis, as well as a staunch advocate for online privacy. In interviews, Durov has downplayed extremists' use of Telegram and said that the vast majority of its users are on the platform for legitimate reasons. He rejects the idea of giving security officials back-door access to the app, claiming that even if Telegram were completely shut down it would do little to stop terrorists from communicating.
Despite Durov's opposition to government interference and restriction of online freedom, Telegram does make attempts to shut down pro-ISIS channels ― it closed down 78 following the November 2015 Paris attacks and since then has shuttered hundreds more.
But the company has been less successful in preventing pro-ISIS activity than platforms like Twitter, which has shut down over 360,000 accounts for promoting terrorism since mid-2015.
The shift to Telegram is also part of ISIS's larger movement towards private networks and the so-called dark web. Experts say that as social media companies lagged behind in addressing extremism on their platforms, terrorist groups have gotten increasingly proficient at altering their communications strategies.
"The learning curve is now very fast, once it took them years to adapt to a new platform or a new media. Now they do it within months," Weimann said.