Samsung Galaxy users are at risk of being spied on by hackers through their phones cameras.
A security flaw means they could also listen to them through the phone's microphone and read all their texts.
It is thought up to half a billion phone users could be affected worldwide, including owners of the newest Samsung Galaxy S6 handsets.
The flaw was revealed by security expert Ryan Welton at a conference in London.
A spokesman for Samsung said they were aware of the issue and would roll out security updates in the next few days.
They added: "Samsung takes emerging security threats very seriously.
"It is important to note that the phone’s core functions (kernel) were not affected by the reported issue due to the protection of the Samsung KNOX platform in all S4 models and above.
"Samsung KNOX also has the capability to update the security policy of the phones, over-the-air, to invalidate any remaining potential vulnerabilities caused by this issue.
"In addition to the Security Policy update, we are also working with SwiftKey to address potential risks going forward."