The Signal chat service cannot be used properly due to interference problems.
The developer of the app reports this on Twitter.
"Signal is experiencing technical problems," the service writes.
"We are working hard to fix everything as quickly as possible."
Signal is experiencing technical difficulties.
We are working hard to restore service as quickly as possible.
Author Signalapp Moment of Places 16:33 - 15 January 2021
Signal is a messaging service similar to WhatsApp, Telegram and iMessage.
Signal's emphasis is on privacy: through the use of specialized encryption, messages cannot simply be intercepted by outsiders.
Strong growth after changes to WhatsApp policy
A cause for the outage is unknown, but Signal recently saw its user base grow sharply.
This happened shortly after competitor WhatsApp introduced controversial privacy rules, allowing data from non-European users to be shared with Facebook.
Tesla CEO Elon Musk recently called on his Twitter followers to switch to Signal.
See also: Telegram reaches 500 million users after commotion over WhatsApp