The Gemalto hack, by the U.S. National Security Agency and the U.K. Government Communications Headquarters (GCHQ), allowed the two spy agencies to monitor a large portion of the world's mobile phone voice and data traffic, according to a story in The Intercept.
The hack was detailed in a 2010 GCHQ document leaked by former NSA contractor Edward Snowden, the story said.
It's unclear how much mobile traffic the two agencies intercepted after the reported hack.
Gemalto, based in the Netherlands, produces about 2 billion SIM cards a year. About 450 mobile carriers, including AT&T, T-Mobile, Verizon Wireless and Sprint, use the company's SIM cards.
With the compromised encryption keys, the surveillance agencies would be able to monitor mobile communications without the approval of the carriers or foreign governments, The Intercept story said. The encryption keys would allow the agencies to intercept mobile traffic without court-ordered warrants or wiretaps, the story said.
Representatives of the NSA and Gemalto did not immediately respond to requests for comments on the story. Gemalto's website was down Thursday afternoon.
Gemalto was unaware of the penetration of its systems, the company told The Intercept. The company is "disturbed" about the possibility, Paul Beverly, a Gemalto executive vice president, told the publication.
GCHQ compromised Gemalto's computer networks and installed malware on several computers, The Intercept story said, quoting a slide from the U.K. intelligence agency provided by Snowden. At the time GCHQ believed it had access to the company's "entire network," the slide said.
GCHQ also said it had access to billing servers of mobile carriers, allowing it to manipulate customer charges in an effort to hide surveillance on phones, the story said.
Grant Gross covers technology and telecom policy in the U.S. government for The IDG News Service. Follow Grant on Twitter at GrantGross. Grant's email address is grant_gross@idg.com.