WhatsApp users have been urged to update their app immediately after it was hit by one of the worst security bugs ever seen.
The flaw allows the app to be attacked by just leaving a missed call.
Once hit, your smartphone is compromised without you even knowing it.
The technology to use the attack appears to have been created by an Israeli company that sells technology exploits to governments, allowing them to spy on citizens.
WhatsApp has rushed to roll out a security fix amid concerns that hackers could inject surveillance software on to phones via the call function.
The company, which is owned by Facebook , discovered a vulnerability that allowed attackers to install malicious code on iPhones and Android phones by ringing up a target device.
They say the attack bore a resemblance to spyware developed for intelligence agencies.
WhatsApp has around 1.5 billion users around the world and it released a software update on Monday night.
A spokesman told the Financial Times: ‘We believe a select number of users were targeted through this vulnerability by an advanced cyber actor.
‘This attack has all the hallmarks of a private company known to work with governments to deliver spyware that reportedly takes over the functions of mobile phone operating systems.
‘We have briefed a number of human rights organisations to share the information we can, and to work with them to notify civil society.’
How do I install the new WhatsApp update?
Some phones will receive a notification message from WhatsApp, urging you to update the software to the latest available version.
Not all customers will, however.
If you have an iPhone, go to the App Store and click updates. When you find Whatsapp, tap the update button next to the app. You phone should then update.
If you own an Android phone, click on Play Store, then on the menu button.
Under My apps and games, tap update next to WhatsApp Messenger.