Although the Telegram messaging application provides a communication encryption feature, it is still able to expose information that may make a user insecure to stalking efforts. These information are not immediately available. The stalker still has to use an external client to be able to view the victim's metadata - however, the fact remains that it can be done.
Personal safety becomes threatened because the user and any other user do not have to be mutual contacts to be added into each other's list. As long as the phone number is provided, anybody can add anyone as a phonebook contact and correspondingly as a Telegram contact.
If the stalker adds the victim's number to their phone book, the victim also automatically shows up as a Telegram contact. From that point, the stalker can already use the third party command line interface (CLI) client to monitor the victim and the victim's contacts, the frequency of communications and even the time and date of these exchanges. Similarly, the stalker can also add the contact that the victim is communicating with and do the same to them.
Sony Mobile Communications consultant Ola Flisback says that what further compounds this vulnerability that he assessed is the fact that neither the victim nor the victim's contact will ever know that they are being monitored because as long as the stalker is not in their phonebook, the stalker will never even show in either of their Telegram contacts list.
Markus Ra, speaking on behalf of Telegram, however clarifies that a user's 'Last Seen' details can actually be hidden by modifying the account's privacy and security settings. This then applies the restriction even up to the API level, after which the metadata is protected and is no longer vulnerable to attackers.
The Telegram service was initially developed and launched by Russian brothers Nikolai and Pavel Durov, who also founded Russia's widest social network - VK. The app came under heavy public scrutiny recently when members of terrorist group ISIS/ISIL came to be known as among the avid users of Telegram.
