The Android version of Microsoft’s voice-driven personal assistant Cortana has accidentally been leaked.
The software was not supposed to be released until 29 July when Windows 10 is due to be released.
An early version of the Cortana app was found online over the weekend and has been widely shared.
Despite being an early version, reports from people who have installed and tested it said it was similar to that seen on Windows handsets.
Cortana was originally developed for Windows, but earlier this year, Microsoft said it planned to make a version that worked on phones running Google’s Android operating system and Apple’s iOS.
The leaked software worked without crashing on a Nexus 5 handset running Android 5.1, said Peter Bright of tech news site Ars Technica who tested the app over the weekend.
Mr Bright said Cortana provided alerts and information about weather, traffic, places to eat and reminders about forthcoming appointments. It could also transcribe speech into emails and text messages.
On Windows devices, Cortana can be brought to life by saying, “Hey Cortana”, as the application is constantly listening for a such a prompt.
However, Android and Apple customers have to activate the app if they want to use it. On both, Cortana can be quizzed by asking questions by typing text or voice.
Mr Bright said Cortana on Android lacked some features found on the Windows version. For instance, he said, it could not listen for music or read emails for flight numbers or parcel delivery information. It also lacked some privacy functions that stopped it springing into life when users were busy or asleep.
Microsoft said it wanted to make the application work across lots of different devices to give people a common experience no matter where they used it.
It has started a beta programme for the software that lets people in the US who have a Windows Insider account try Cortana before the official release next week.
However, said Mr Bright, it was not clear that people would stick with it on Android. For the moment, he said, Google Now was “better integrated and more capable”.