A vulnerability discovered in Facebook’s WhatsApp messaging app is being exploited to inject commercial spyware onto Android and iOS phones by simply calling the target, reports The Financial Times. The spyware, developed by Israel’s secretive NSO group, can be installed without trace and without the target answering the call, according to security researchers and confirmed by WhatsApp.

Once installed, the spyware can turn on a phone’s camera and mic, scan emails and messages, and collect the user’s location data. WhatsApp is urging its 1.5 billion global users to update the app immediately to close the security hole.

“WhatsApp encourages people to upgrade to the latest version of our app, as well as keep their mobile operating system up to date, to protect against potential targeted exploits designed to compromise information stored on mobile devices,” said WhatsApp in a statement.

Pegasus can turn on a phone’s camera and mic, scan emails and messages, and collect location data

Facebook issued a security advisory on Monday apparently in relation to the WhatsApp vulnerability. “A buffer overflow vulnerability in WhatsApp VOIP stack allowed remote code execution via specially crafted series of SRTCP packets sent to a target phone number,” according to the advisory. The vulnerability exists in the following versions of WhatsApp:

WhatsApp for Android prior to v2.19.134

WhatsApp Business for Android prior to v2.19.44

WhatsApp for iOS prior to v2.19.51

WhatsApp Business for iOS prior to v2.19.51

WhatsApp for Windows Phone prior to v2.18.348

WhatsApp for Tizen prior to v2.18.15

The vulnerability discovered in early May, was targeted as recently as Sunday when a UK-based human rights lawyer was attacked by NSO’s flagship Pegasus program, according to researchers at Citizens Lab. The attack was blocked by WhatsApp. WhatsApp is investigating the situation but is so far unable to estimate the number of phones successfully targeted by the exploit, said a source speaking to the FT.

“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,” said WhatsApp in a statement provided to The Financial Times. “We have briefed a number of human rights organizations to share the information we can, and to work with them to notify civil society.”

NSO says it sells Pegasus to governments and law enforcement agencies to help fight terrorism and crime. But that hasn’t stopped the company’s spyware from being used by countries, organizations, and individuals undeterred by human rights concerns. In 2016, NSO spyware was implicated in an attack on Emirati human rights activist named Ahmed Mansoor. In 2018, NSO’s spyware was aimed at prominent TV journalist Carmen Aristegui and 11 others while investigating a scandal involving the Mexican President.

Researchers claim that NSO’s powerful spyware has been used by as many as 45 countries to aid in the persecution of dissidents, journalists, and other innocent civilians.

Update May 14th, 6:20AM ET: Added additional details about WhatsApp versions affected.