BERLIN: For anyone who uses the Signal messenger app, it's important that you activate the PIN feature. This number can be used not only to restore contacts and account settings if you lose or change your device, it also plays an important role in security.

That's because the PIN is the basis for a registration block that prevents strangers from logging in to Signal using your phone number. Signal advises all users to switch on the PIN and registration lock.

A recent phishing attack on a service provider that works with Signal resulted in almost 2,000 phone numbers that were registered with Signal being stolen.

The attackers couldn't have gained access to chats, profile information or contact lists, because this data is only stored locally on the device and can only be restored using the PIN.

However, the attackers could have re-registered the stolen phone numbers on other devices and then received and sent messages using those accounts. In response Signal has unregistered those accounts and asked the users to register again.

WhatsApp offers similar PIN protection against unauthorised registration of one's own account. Two-step verification is used to set it up and the PIN can be reset by email if you forget it. In the case of Signal, the PIN can neither be reset nor restored.

 - dpa