If you were to ask me what most distinguishes the terrorist group led by Fetullah Gülen and orchestrated the July 15 coup attempt in Turkey, I would respond with one word: Deception.

Since the 1970s, tens of thousands of the group's operatives infiltrated the Turkish government – and all of them were trained to hide their identity. It was through deception that Turkey's strategic institutions, in particular the national security machinery, were brought under Gülen's control. Once in charge, members of the Pennsylvania-based criminal gang abused their official powers to illegally eavesdrop on the communications of hundreds of thousands of citizens. At the same time, Gülen's judges and prosecutors conspired against thousands of innocent people, while protecting thousands of criminals following the organization's orders.

Over the past six years, the Turkish people developed a deeper understanding of Gülen's infiltration of state institutions. However, the July 15 coup attempt revealed that the group in fact had far more power.

The failed coup shocked the public in two ways: First, many people found it difficult to believe that Gülenists were ambitious enough to attempt a violent throw of Turkey's government. Moreover, everyone already knew that the group had infiltrated state institutions – but they were dead wrong about the extent of their power.

In the failed coup's aftermath, it became clear that Gülenist operatives controlled roughly one-third of Turkey's military hierarchy. Even President Recep Tayyip Erdoğan's aide de camp, who accompanied the Turkish leader everywhere, turned out to be one of Gülen's people. At the same time, the authorities identified close associates of military Chief of General Staff Gen. Hulusi Akar and other Turkish generals as Gülenists.

Gen. Hakan Evrim, known by his colleagues as a secular-minded military officer, revealed his true identity to Gen. Akar hours after tanks rolled down the streets of Istanbul and Ankara, when he offered Turkey's top military official a phone call with Gülen himself in the hopes of getting him on board.

The deception proved so successful that many Turks compared Gülenist operatives to the Assassins – a medieval secret order best known for high-profile assassinations and the absolute devotion of its operatives to their leader. Just as people start to believe they have learned everything about the group, a new revelation comes to shock them.

The arrest of Kadir Güntepe, the former governor of Beytüşşebab county in Şırnak, is a case in point. The official originally caught the Turkish public's attention for his efforts to curb the PKK's influence over his district. On social media, Güntepe rose to popularity as a nationalist and conservative statesman, hailed by the media as a hero after the PKK terrorists reportedly issued a death threat against him.

Understandably, a lot of people were caught by surprise when Kadir Güntepe was detained by the police last week over his links to Gülen's group. According to media reports, he repeatedly communicated with senior Gülenists in person and over the phone, and had used Bylock, the group's encrypted messaging app, in the past. Overnight, the hero had become villain.

Those who believe that the Gülenist threat has been neutralized thanks to security operations and the firing of tens of thousands of public officials should draw lessons from Güntepe's arrest. While Gülen's operatives developed immense expertise by concealing their true identities, the full extent of the official investigation into their network remains unknown to the public – and will remain unclear until every investigation is finished and every case is closed. At a time when Gülenists have started issuing new, thinly-veiled threats against Turkey, the Turkish people cannot afford to underestimate them.