More than a dozen Telegram accounts have been compromised by threat actors in Iran. Moreover, the phone numbers of users have been identified. The case is considered to be the greatest breach of the cyber-attacks.
According to the experts Collin Anderson and Claudio Guarnieri, the cyber-attack which has happened previously this year exposes to a risk all the activists and journalists in Iran where approximately 20 million people use the messenger.
As the researchers have stated, the main vulnerability that can lead to these consequences is the use of SMS messages for activating a new device. When a user wants to use Telegram from another device, he should enter authorization codes sent by company via SMS. The messages can be caught by the phone company for selling the hackers.
SMS verification seems to be vulnerable in any country where cellphone companies are affected by the government.
Rocket Kitten is considered to be the hackers. Their campaign reflected the interests of Iran public authorities. But nobody can state they are supported by the government.
The representatives of Telegram said that only public information was available for attackers while 15 million user accounts were not compromised. Now check is impossible as there are some restrictions concerning API.
As for the security, people were caution about potential SMS interception. It would be better to use double authentication for preventing the attacks.