Tens of thousands of documents, containing names, addresses, telephone numbers, and family contacts of Islamic State jihadis, have been presented to British TV network Sky News.
Nationals from at least 51 countries, including the United States, had to give up their most personal information as they joined the terror organization.
Only when the 23-question form was filled in were they inducted into IS.
A lot of the names and their new Islamic State names on the registration forms are well-known.
But the key breakthrough from the documents is the revealing of the identities of a number of previously unknown jihadis in the United States, Canada, the UK, across northern Europe, the Middle East, and North Africa.
Their whereabouts are crucial to breaking the organization and preventing further terror attacks.
Some of the telephone numbers on the list are still active and it is believed that although many will be family members, a significant number are used by the jihadis themselves.
The files were passed to Sky News on a memory stick stolen from the head of Islamic State's internal security police, an organization described by insiders as the group's version of Hitler's SS.