"An Israeli firm accused of supplying tools for spying on human-rights activists and journalists now faces claims that its technology can use a security hole in WhatsApp, the messaging app used by 1.5 billion people, to break into the digital communications of iPhone and Android phone users (Warning: source may be paywalled; alternative source). Security researchers said they had found so-called spyware -- designed to take advantage of the WhatsApp flaw -- that bears the characteristics of technology from the company, the NSO Group."

WhatsApp uses code which cannot be independently audited, therefore, it should be considered 100% insecure.