Telegram is a cloud-based messaging app where messages "self-destruct" after a certain period of time. Telegram In response to Anonymous’ recent hacking threats, the extremist militant group ISIS is encouraging its followers to start using a popular messaging app, where it’s providing “instructions” on how to avoid being hacked.

An ISIS-affiliated account on the popular messaging app Telegram — which has more than 50 million users sending one billion messages a day, according to The Daily Beast — provided instructions to followers in both Arabic and English, which was then forwarded to other ISIS-affiliated channels on Telegram.

The instructions told followers to not open any links unless they were sure of the source, and change IP addresses “constantly.” ISIS also told people “do not talk to people [you] don’t know on Telegram” or through direct messages on Twitter.

This heightened alert on ISIS’ part is due to Anonymous, which declared “war” on the extremist group after Friday’s attacks in Paris and claims to have helped Twitter shut down over 5,500 pro-ISIS accounts on the network.

In the past few days, Anonymous has also leaked personal information about ISIS supporters, including their names and physical addresses, and the group is even posting public guides for anyone that wants to search, find, or hack pro-ISIS websites.

Still, government officials are concerned about ISIS increasing its usage of messaging apps like Telegram, which are fully encrypted and effectively impossible to snoop on. Messages on Telegram, like Snapchat, “self-destruct” after a certain period of time.

“There are a lot of technological capabilities that are available right now that make it exceptionally difficult, both technically as well as legally, for intelligence and security services to have the insight they need to uncover [terrorist activities],” CIA director John Brennan said at a Monday security conference in Washington (via NPR).

“I do think this is a time for particularly Europe, as well as here in the United States, for us to take a look and see whether or not there have been some inadvertent or intentional gaps that have been created in the ability of intelligence and security services to protect the people that they are asked to serve.”

As governments try to balance surveillance with data protection and privacy, secure messaging apps like Telegram will continue to be popular, particularly among the youth that are attracted to the idea of ephemeral messaging. On the plus side, Reuters reports Iran arrested administrators of more than 20 different groups on Telegram this week for spreading “immoral” content.