TextSecure was developed by Whisper Systems, which Twitter acquired last month. The tool works by encrypting text messages before they are sent, adding a layer of security that businesses will appreciate, particularly as it is now open source like Android itself.

It is interesting that Twitter did not make this part of its Android app features, nor expand the technology for its web site. Usually when companies buy good software they pull it from rival systems and use it to attract customers, but there will be no direct benefit for Twitter, aside from a good reputation, in releasing the software as open source.

The move suggests a new direction for Twitter that could see it expand into a software company with influences in many digital markets.

"We've always been interested in the ability for individuals and organisations to communicate freely and securely," said Whisper Systems in a statement.

"In the year and a half since Whisper Systems launched TextSecure, we've received an enormous amount of thanks, feedback and encouraging stories from users who have employed TextSecure towards those ends.

"We hope that, as an open source project, TextSecure will reach even more people, with an even larger number of contributors working to make it a great product."

Whisper Systems might be planning to open source the rest of its software, having indicated that it will open source its code in an "iterative fashion", delayed mainly by legal requirements.

This means that Twitter software for encrypted calls, backups and network and device security could join the ranks of widely shared open source software applications.

The TextSecure source code is available at GitHub.