WhatsApp today disclosed a vulnerability that allowed hackers to remotely exploit a bug in the app's audio call system to access sensitive information on an iPhone or Android device.

According to The New York Times, attackers were able to insert malicious code into WhatsApp, allowing them to steal data, regardless of whether or not a WhatsApp phone call was answered.

Security researchers said that the spyware that took advantage of this flaw featured characteristics of the Pegasus spyware from NSO Group, which is normally licensed to governments who purchase the spyware for installing on the devices of individuals who are the target of an investigation.

Description: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. Affected Versions: The issue affects 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, and WhatsApp for Tizen prior to v2.18.15.

The vulnerability was described by WhatsApp as "nontrivial to deploy, limiting it to advanced and highly motivated actors," but it's not clear how long the security flaw was available nor how many people were affected. It was used to target a London lawyer who has been involved in lawsuits against the NSO Group, and security researchers believe others could have been targeted as well.

WhatsApp engineers "worked around the clock" to address the vulnerability, and made a patch available on Monday. The initial vulnerability was discovered ten days ago after WhatsApp found abnormal voice calling activity following complaints from the aforementioned lawyer. WhatsApp says that it has notified the Department of Justice and a "number of human rights organizations" about the issue.

Update: Reader comments suggested that some of the wording in this article was confusing or misleading, so we have updated it to make sure the details of the vulnerability are clear. Specifically, this issue impacted WhatsApp, not the iOS operating system.