Facebook's WhatsApp urged users to upgrade to the latest version of its popular messaging app following a report that users could be vulnerable to having malicious spyware installed on phones without their knowledge.
WhatsApp, one of the most popular messaging tools, is used by 1.5 billion people monthly and it has touted its high level of security and privacy, with messages on its platform being encrypted end to end.
"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," a spokesman said.
"We are constantly working alongside industry partners to provide the latest security enhancements to help protect our users," he said. WhatsApp did not elaborate further.
The Financial Times reported that a vulnerability in WhatsApp allowed attackers to inject spyware on phones by ringing up targets using the app's phone call function.
It said the spyware was developed by Israeli cyber surveillance company NSO Group and affects both Android and iPhones. The FT said WhatsApp could not yet give an estimate for how many phone were targeted.
The FT reported that teams of engineers had worked around the clock in San Francisco and London to close the vulnerability and it began rolling out a fix to its servers on Friday last week and issued a patch for customers on Monday.
Asked about the report, NSO said its technology is licensed to authorised government agencies "for the sole purpose of fighting crime and terror," and that it does not operate the system itself while having a rigorous licensing and vetting process.
"We investigate any credible allegations of misuse and if necessary, we take action, including shutting down the system. 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," the company said.
WhatsApp disclosed the issue to the US Department of Justice last week, the FT said.
Social media giant Facebook bought WhatsApp in 2014 for $19 billion.
Facebook co-founder Chris Hughes last week wrote in The New York Times that fellow co-founder Mark Zuckerberg had far too much influence by controlling Facebook, Instagram and WhatsApp, three core communications platforms, and called for the company to be broken up.