Today [20/12] Zaman is a Turkish daily and part of the Gülen organization. As such it is currently in opposition to the Turkish president Erdogan and some of his policies. So take this with a grain of salt:
During the meetings between Turkish officials and Barzani in Ankara, Barzani spoke on the 150 ISIL militants of Turkish origin who had been captured by Kurdish peshmerga forces during clashes with ISIL. According to sources, Barzani said some ISIL members captured by the peshmerga had identified themselves as members of MİT and he requested that MİT head Fidan clarify the issue. Barzani also sought assistance from Ankara to remove 500 Turkish nationals in Mosul who are in leading positions in ISIL.
The MIT is the Turkish secret service. It is certainly not the only spy organization whicht has infiltrated the Islamic State. But as Turkey has been the rear base and travel route for the Islamic State and its members the MIT is likely the service with the biggest contingent.
How any spies and/or operators does it have within the Islamic State structures? Even more important - how influential are these within the Islamic State hierarchies?
The Kurdish organizations within Turkey believe that the two big Islamic State attacks on mostly Kurdish rallies, in Suruc and in Ankara, were intended to support Erdogan's reelection. Influential MIT agents within the Islamic State would have been be part of such conspiracies.