Terror investigators grapple with Telegram app

The messaging platform's strong encryption makes it a favorite of IS

Smartphone app Telegram, favored by the Islamic State group thanks to the encrypted messaging it offers, is proving a headache for French anti-terror investigators.

The free-to-download instant messenger, which allows people to exchange messages, photos and videos in groups of up to 5,000 people, has attracted some 100 million users since its launch in 2013.