Social media stock. Stock photo of the WhatsApp app icon on a smartphone. Picture date: Friday March 15, 2019. See PA story TECHNOLOGY SocialMedia. Photo credit should read: Nick Ansell/PA Wire URN:41898780 (Press Association via AP Images)
PHOTO: Nick Ansell/AP
Social media stock. Stock photo of the WhatsApp app icon on a smartphone. Picture date: Friday March 15, 2019. See PA story TECHNOLOGY SocialMedia. Photo credit should read: Nick Ansell/PA Wire URN:41898780 (Press Association via AP Images)
Now playing
02:08
WhatsApp warns of spyware vulnerability
marketplace africa covid 19 appliance manufacture ventilators spc_00031216.png
marketplace africa covid 19 appliance manufacture ventilators spc_00031216.png
Now playing
03:48
How Covid-19 pushed this appliance giant towards the health care space
PHOTO: MyHeritage
Now playing
01:01
Watch old photos come to life using AI
Now playing
01:26
No, Tom Cruise isn't on TikTok. It's a deepfake
A Facebook employee walks by a sign displaying the "like" sign at Facebook's corporate headquarters campus in Menlo Park, California, on October 23, 2019. (Photo by Josh Edelson / AFP) (Photo by JOSH EDELSON/AFP via Getty Images)
PHOTO: Josh Edelson/AFP/Getty Images
A Facebook employee walks by a sign displaying the "like" sign at Facebook's corporate headquarters campus in Menlo Park, California, on October 23, 2019. (Photo by Josh Edelson / AFP) (Photo by JOSH EDELSON/AFP via Getty Images)
Now playing
02:36
Facebook to restore news in Australia
Now playing
02:57
Why Microsoft backs Australia's pay for news proposal
MADISON, WI - NOVEMBER 05:  U.S. President Barack Obama and rocker Bruce Springsteen wave to a crowd of 18,000 people during a rally on the last day of campaigning in the general election November 5, 2012 in Madison, Wisconsin. Obama and his opponent, Republican presidential nominee and former Massachusetts Gov. Mitt Romney are stumping from one 'swing state' to the next in a last-minute rush to persuade undecided voters.  (Photo by Chip Somodevilla/Getty Images)
PHOTO: Chip Somodevilla/Getty Images
MADISON, WI - NOVEMBER 05: U.S. President Barack Obama and rocker Bruce Springsteen wave to a crowd of 18,000 people during a rally on the last day of campaigning in the general election November 5, 2012 in Madison, Wisconsin. Obama and his opponent, Republican presidential nominee and former Massachusetts Gov. Mitt Romney are stumping from one 'swing state' to the next in a last-minute rush to persuade undecided voters. (Photo by Chip Somodevilla/Getty Images)
Now playing
01:26
Barack Obama and Bruce Springsteen team up for new podcast
Find Solution AI facial expression reading software mapping facial muscles to assess emotion
PHOTO: Shutterstock/Find Solution AI
Find Solution AI facial expression reading software mapping facial muscles to assess emotion
Now playing
03:54
How AI that reads emotions is changing the online classroom
This illustration picture shows the social media website from Parler displayed on a computer screen in Arlington, Virginia on July 2, 2020. - Amid rising turmoil in social media, recently formed social network Parler is gaining with prominent political conservatives who claim their voices are being silenced by Silicon Valley giants. Parler, founded in Nevada in 2018, bills itself as an alternative to "ideological suppression" at other social networks. (Photo by Olivier Douliery/AFP/Getty Images)
PHOTO: Olivier Douliery/AFP/Getty Images
This illustration picture shows the social media website from Parler displayed on a computer screen in Arlington, Virginia on July 2, 2020. - Amid rising turmoil in social media, recently formed social network Parler is gaining with prominent political conservatives who claim their voices are being silenced by Silicon Valley giants. Parler, founded in Nevada in 2018, bills itself as an alternative to "ideological suppression" at other social networks. (Photo by Olivier Douliery/AFP/Getty Images)
Now playing
01:25
Parler's website is back online
screengrab singapore contact tracing app
PHOTO: Government Technology Agency of Singapore
screengrab singapore contact tracing app
Now playing
03:07
How Singapore's contact tracing technology undermines citizen's trust
PHOTO: Boston Dynamics
Now playing
01:20
Spot the robot's new arm lets it jump rope (and do serious stuff)
Detail of a mans hand scrolling through Netflix on an Apple iPad Pro, taken on March 6, 2020. (Photo by Phil Barker/Future Publishing via Getty Images)
PHOTO: Future Publishing via Getty Imag
Detail of a mans hand scrolling through Netflix on an Apple iPad Pro, taken on March 6, 2020. (Photo by Phil Barker/Future Publishing via Getty Images)
Now playing
04:27
2020 was supposed to be the year of streaming. Instead, it was the year of Netflix
PHOTO: WCCO
Now playing
01:26
Man donates Nintendo Switches to kids in need with GameStop stock
NEW YORK, NEW YORK - JANUARY 27: GameStop store signage is seen on January 27, 2021 in New York City. Stock shares of videogame retailer GameStop Corp has increased 700% in the past two weeks due to amateur investors. (Photo by Michael M. Santiago/Getty Images)
PHOTO: Michael M. Santiago/Getty Images
NEW YORK, NEW YORK - JANUARY 27: GameStop store signage is seen on January 27, 2021 in New York City. Stock shares of videogame retailer GameStop Corp has increased 700% in the past two weeks due to amateur investors. (Photo by Michael M. Santiago/Getty Images)
Now playing
03:16
GameStop mania shakes up Wall Street
SAN ANSELMO, CALIFORNIA - JANUARY 08: The suspended Twitter account of U.S. President Donald Trump appears on an iPhone screen on January 08, 2021 in San Anselmo, California. Citing the risk of further incitement of violence following an attempted insurrection on Wednesday, Twitter permanently suspended President Donald Trump's account. (Photo Illustration by Justin Sullivan/Getty Images)
PHOTO: Justin Sullivan/Getty Images North America/Getty Images
SAN ANSELMO, CALIFORNIA - JANUARY 08: The suspended Twitter account of U.S. President Donald Trump appears on an iPhone screen on January 08, 2021 in San Anselmo, California. Citing the risk of further incitement of violence following an attempted insurrection on Wednesday, Twitter permanently suspended President Donald Trump's account. (Photo Illustration by Justin Sullivan/Getty Images)
Now playing
04:29
What impact could deplatforming Donald Trump have?
screengrab US social media
PHOTO: Getty Images
screengrab US social media
Now playing
04:35
Tech companies ban Trump, but not other problematic leaders
(CNN Business) —  

WhatsApp has revealed a vulnerability in its system that could have allowed hackers access to its users’ phones, with a London-based human rights lawyer possibly among the targets.

The encrypted messaging service, owned by Facebook (FB), said Monday that it had discovered and fixed the vulnerability the attackers had sought to exploit. The hackers could implant malicious code on a victim’s phone by placing a voice call to the victim on WhatsApp — victims may not even have needed to answer the call for their phone to be infected, an expert told CNN Business.

“The attack has all the hallmarks of a private company reportedly that works with governments to deliver spyware that takes over the functions of mobile phone operating systems,” a WhatsApp spokesperson said in a statement.

While WhatsApp did not name the private company, a source familiar with the investigation into the attack said that company is NSO Group, an Israeli cyber company that has developed a powerful piece of malware designed to spy on its victims.

In a statement provided to CNN on Monday, NSO said, “Under no circumstances would NSO be involved in the operating or identifying of targets of its technology, which is solely operated by intelligence and law enforcement agencies.”

NSO said its technology was licensed to government agencies “for the sole purpose of fighting crime and terror,” adding that those agencies determine how the technology is used without any involvement from the company.

The Financial Times first reported details of the vulnerability.

Human rights activists targeted

Among those believed to have been targeted via WhatsApp is a London-based human rights lawyer, who is advising on a case against NSO. NSO has denied targeting the lawyer.

On Sunday, the lawyer received two calls that John Scott-Railton, a senior researcher at the University of Toronto’s Citizen Lab believes were part of the attack. Citizen Lab is an academic security research group that investigates digital threats to civil society groups and online freedom of expression.

The apparent attempt to breach the lawyer’s phone was not successful, Scott-Railton said, as WhatsApp had patched the vulnerability by Sunday.

Speaking to CNN Business on Tuesday the lawyer, who does not want to be named, said that in March they began receiving suspicious calls on WhatsApp from Swedish and other European phone numbers.

WhatsApp had reached out to Citizen Lab and a number of other groups that work with human rights defenders before publicly acknowledging the attack.

The collaboration between WhatsApp and Citizen Lab helped identify the attempted attack on the London-based lawyer.

Responding specifically to the apparent targeting of the lawyer, NSO Group said in a statement, “NSO would not or could not use its technology in its own right to target any person or organization, including this individual.”

“This is a vulnerability that would have enabled attackers to take over a phone with a missed call,” Scott-Railton said.

In another development before the attack was revealed, Amnesty International announced it would file a petition at the district court of Tel Aviv on Tuesday demanding Israel withdraw NSO’s export license, Amnesty’s lawyer told CNN Business.

The group claims that NSO software “threatens the rights to privacy and to freedom of opinion and expression, in breach of Israel’s obligations under international human rights law.”

It said one of its researchers had been targeted via a WhatsApp message containing NSO’s spying software in 2018 while working on a campaign to release six women’s rights activists detained in Saudi Arabia.

How to update your WhatsApp

WhatsApp said while it has fixed the vulnerability the attackers were exploiting, it is also encouraging users to update to the latest version of the WhatsApp app “out of an abundance of caution.” The company said it has also contacted US law enforcement.

On Monday night, the Democratic National Committee advised 2020 Democratic presidential campaign staff who use WhatsApp to update their apps to the most recent version of the service, a source familiar with the warning told CNN Business.

Ireland’s Data Protection Commission, which supervises Facebook’s activities in Europe, said it had been informed of the vulnerability on Monday, adding it was unclear at this stage whether any EU user data had been affected.

Still, it too urged users to ensure the update WhatsApp on their devices.

Here’s how:

On an iPhone

– Open the App Store and select updates.

– Select “WhatsApp” and Update.

On an Android device

– Open the Play Store and tap on the 3 lines in the upper left corner.

– Select “My apps & games” from the menu.

– Select “WhatsApp” and select Update.

Hadas Gold contributed to this report.