Two instant messaging apps offering top-notch encryption are under the spotlight for their alleged use by the Gülenist Terror Group (FETÖ), whose members are accused of carrying out the July 15 putsch attempt. Authorities are investigating tens of thousands of suspected members of the terror group who used Bylock and Eagle to avoid detection, according to media reports.

Quoted by Turkish media outlets after a meeting with representatives from the two apps two weeks ago, Prime Minister Binali Yıldırım said Gülenists had their own communication network with "some 50,000 members" and they were striving to separate the loyal Gülenists and those with indirect ties to the group. He said investigators were trying to detect members of the cult within the military, bureaucracy and business world in investigations after the coup attempt, which killed hundreds of civilians and security personnel.

The communication network Yıldırım referred to is linked to Bylock and Eagle, according to the media outlets that reported the National Intelligence Organization (MİT), decoded the messages and pinpointed each user. Users who work as civil servants and bureaucrats are now being investigated for their possible links to FETÖ. Several suspects linked to the terror group have already confessed to using Bylock, which was discontinued in 2014.

Tens of thousands of people linked to FETÖ were suspended from state institutions after the coup attempt, while over 4,800 people were dismissed and face criminal charges. Most of those dismissed are members of the judiciary and the military.

Testimonies from Gülenists in the bureaucracy detained after the July 15 putsch attempt point out the prevalence of the use of apps. Prosecutors say Bylock was popular among Gülenists for secretive communications between 2013 and 2015, and after 2015, the terror cult turned to Eagle IM, which offers "256-bit end-to-end AES encryption" for its users, according to the description on the app at the Google Play Store. The app's developers also promise protection from "Man In The Middle" attacks or hacking into chats between two people that enables message altering by one of the two parties. Similarly, Bylock was offering an eight-digit password for users and a highly secure encryption.

Investigations reveal both those in the lower ranks of FETÖ's infiltrators within state institutions and those in the upper echelons of the bureaucracy perused Bylock. A testimony by Sinan Çörekçi shows a senior Gülenist in the northwestern city of Kırklareli installed the app on the phones of those with intimate ties to FETÖ. Çörekçi was a court clerk in the city detained after the coup attempt. He told the prosecutors that Hakan Altun, a Gülenist figure responsible for organizing the infiltration within the local judiciary, told him and others to communicate through Bylock. The same app was found on the cellphone of Dinçer Ural, a brigadier general who acted as a legal adviser to the Chief of the General Staff. Ural was detained for his links to the terror group and has contacted Dilaver Azim, a prominent Gülenist figure according to prosecutors who say Azim was entrusted with controlling the funds to FETÖ. Doğan News Agency reported that Ural and Azim regularly exchanged messages via Bylock between 2011 and 2015. A report in the Habertürk daily says MİT decoded some 18 million encrypted messages between more than 50,000 people. The same news article says about 1,000 people using Bylock were among those detained in operations against FETÖ.

FETÖ, which is also accused of a string of crimes ranging from illegal wiretapping, installing hidden cameras in politicians' houses and fabricating evidence, is known for its prevalent use of apps for encrypted and open messaging.