The Chinese mobile firm, Xiaomi, has apologised to its customers after privacy concerns were raised over its Cloud Messaging service.
Unhashed phone numbers were being used temporarily to check whether message recipients were online, but were not being stored, according to the company.
Hugo Barra, VP of Xiaomi, said: "As we believe it is our top priority to protect user data and privacy, we have decided to make MIUI Cloud Messaging an opt-in service and no longer automatically activate users."
The upgrade was released this Sunday, following adverse publicity created by an F-Secure report and various media in Taiwan.
Barra added that users of the service will now have their phone numbers encrypted, and reiterated that the data would not be stored online.
"We apologise for any concern caused to our users and Mi [phone] fans," he said.
"We would also like to thank the media and users who have been sending us feedback and suggestions, allowing us to improve and provide better internet services."