In 2016, the company revealed that it had more than one billion users.
While it might not be the most secure, it can offer a good level of protection even in times of controversy.
And although Facebook insists that it couldn’t read your Whats App messages even if it wanted to, critics have been suspicious since the buy – since Facebook's entire platform depends on data and advertising, and its own Messenger service is infamously intrusive.
In terms of security, it's important to distinguish pure secure messaging apps from apps that happen to have some security, for instance the hugely popular Whats App and Snap Chat.
Users will be able to set up a backup email in case they forget the passcode.
It's unlikely to inspire enormous confidence in Whats App as a secure platform, but it is a small nod towards security for personal use.
Home secretary Amber Rudd has called for technology companies to build back door into their encrypted content for security services to use when they require access in the fight against terrorism.
The applications have been a cottage industry for desktop computers for years, usually for secure email or instant messaging, but the arrival of mobile platforms has given them the sort of kick that is leading many to dream of reaching the mainstream.
The software used to be seen as the preserve of the technical users with a paranoid bent or political dissidents, but ayears.
In March, Wiki Leaks released information documenting over 8,000 CIA spying files in its 'Vault 7' collection.
Reports surrounding this claimed that the CIA was able to easily bypass Whats App's (and Signal's) security systems and read user messages.