WhatsApp developers discover 'attack'
WhatsApp are being urged to update their app immediately after being hacked.
The Financial Times reports an Israeli security firm was responsible for using the calls feature to inject spyware onto a 'select number' of users phones.
It impacted both iOS and Android devices, according to a security note from Facebook.
As a result, WhatsApp has urged all of its 1.5 billion users to update their apps as an added precaution.