Hacktivists have exposed those subscribing to ISIS backed newsletters from the terror group's official news site. HackRead has a nice writeup on this:
"A group of Muslim hacktivists from Ahlus Sunnah Wal Jamaah, the Sunni sect of Islam and going by the online handle of Di5s3nSi0N hacked the official website of ISIS/ISIL (Daesh) and leaked a list of more than 2000 people who had subscribed to the site’s newsletter and updates through email.
A week ago, the targeted website Amaq which also works as a news agency for the terrorist organization claimed that it was facing increasing cyber attacks, therefore, it has increased its security and now their admins can tackle “any type of hack.”
Apparently, it could not handle the hack by this group.