The messaging app Snapchat has introduced end-to-end encryption, preventing the photos shared between its users being intercepted.
The app, which has 186 million users and an estimated 16 million in the UK, is encrypting billions of messages a day.
End-to-end encryption scrambles a message as it travels over an internet network so it can be read only by the recipient. Messages that are not encrypted can potentially be picked up by security services or hackers.
Other messaging apps including WhatsApp and iMessage use encryption, claiming the technology keeps users secure.
However, politicians and security chiefs have said it risks allowing criminals to communicate safely.