Israeli surveillance firm NSO Group offered a United States mobile security company “bags of cash” to gain access to its signalling network, The Washington Post and other media outlets have reported, citing a whistle-blower.

Gary Miller, a former executive at California-based Mobileum, said in disclosures to the US Department of Justice that NSO Group made the offer to the company during a 2017 conference call, the Post said on Tuesday.

The newspaper reported that Miller also shared details of the call with US Congressman Ted Lieu, who has raised the issue with the Justice Department.

The Guardian newspaper and journalism non-profit Forbidden Stories, which are members of a media consortium investigating NSO Group known as the Pegasus Project, also reported on the allegations on Tuesday.

The news outlets said NSO Group was trying to access a signalling network known as SS7.

“The privacy implications to Americans and national security implications to America of NSO Group accessing mobile operator signalling networks are vast and alarming,” Lieu wrote in a letter to the Justice Department, according to The Guardian.

NSO Group denied the allegations, telling The Washington Post that the company “does not do business using cash as a form of payment”.

The Israeli company sparked outrage from rights groups last year after an investigation by international media outlets revealed the firm’s Pegasus spyware was used by security forces and authoritarian governments in several countries.

The administration of US President Joe Biden imposed sanctions on NSO Group in November, accusing the firm of enabling “transnational repression”. But the company has repeatedly denied wrongdoing, insisting that its surveillance tools are designed to track criminals and “terrorists”.

Lieu publicly confirmed his call for an investigation on Tuesday.

“The NSO Group, which sells phone hacking software, tried to gain access to cellular networks by offering ‘bags of cash’ according to a whistleblower. I made a criminal referral to [the Justice Department],” he wrote on Twitter.

“And with the #SS7 security flaw in cell networks, no one’s phone is safe.”

The NSO Group, which sells phone hacking software, tried to gain access to cellular networks by offering “bags of cash” according to a whistleblower. I made a criminal referral to @TheJusticeDept.

And with the #SS7 security flaw in cell networks, no one’s phone is safe. https://t.co/WxlJL5yrMi

— Ted Lieu (@tedlieu) February 1, 2022

Miller, the whistle-blower, now works for the University of Toronto’s Citizen Lab, which tracks hacking and surveillance, including NSO Group’s activities.

“The NSO Group was specifically interested in the mobile networks,” The Washington Post quoted Miller as saying. “They stated explicitly that their product was designed for surveillance and it was designed to surveil not the good guys but the bad guys.”

Citing anonymous sources, both The Guardian and the Post reported that the Justice Department is already investigating NSO Group for possible illegal hacking of phones and use of computer networks.

The Justice Department did not immediately respond to Al Jazeera’s request for comment on Tuesday afternoon.

NSO Group is facing two separate civil lawsuits in US courts from WhatsApp and Apple Inc, which have accused the Israeli firm of illegally breaching their networks.

By block head

Block Head is a blockchain journalist.