Spy agencies from the United States and the United Kingdom have jointly hacked into the world's largest manufacturer of SIM cards to monitor mobile phones all over the world, according to a report by The Intercept.

The organization, which was co-founded by the man who worked with Edward Snowden to expose the large scale American National Security Agency (NSA) spying program Glenn Greenwald, has cited documents to back up their claim that SIMS manufactured by Gemalto were breached.

Gemalto, based in the Netherlands, is the largest manufacturer of SIM cards in the world. It reportedly produces as many as two billion chips every year for around 450 clients from all over the world, including Sprint (S), Verizon (VZ, Tech30), T-Mobile (TMUS) and AT&T (T, Tech30) .

The Dutch company also manufactures chips that are used in credit cards issued by more than 3,000 different financial institutions from around the world. Gemalto, a company which prides itself on its state-of-the-art digital security, claims it was not aware of the hackings that reportedly took place between 2010 and 2011.

In a statement, the company said it is investigating the report. It went on to say: "We cannot at this early stage verify the findings of the publication and had no prior knowledge that these agencies were conducting this operation." Its shares fell 7.5% in Europe in the morning session.

The report issued by The Intercept is based upon classified reports that were leaked by former NSA contractor Edward Snowden. The American fugitive, who is currently living in Russia under asylum, is wanted in the United States for theft of government property and espionage. He leaked large volumes of files showing the United States government's spying operations in 2013.

Human rights groups have criticized what they are calling a serious breach of privacy. They are also warning that the attacks may still be ongoing, as the NSA continues to operate its spying programs with the backing of the United States government.