Apple boss Tim Cook has blasted the US government after it demanded that the tech giant help unlock an iPhone that is implicated in the FBI investigation into the San Bernadino shooting.

In a letter to customers, Cook wrote: "Specifically, the FBI wants us to make a new version of the iPhone operating system, circumventing several important security features, and install it on an iPhone recovered during the investigation. In the wrong hands, this software — which does not exist today — would have the potential to unlock any iPhone in someone’s physical possession."

He calls the implications of the request "chilling" and said that they create a dangerous precedent because the government "would have the power to reach into anyone’s device to capture their data".

Jacob Ginsberg, Senior Director at secure encryption provider Echoworx, said: "Apple has every right to say no to the government in this instance, and technology providers across the world will agree with it on the grounds that it is going to put them on very shaky ground. The government is asking Apple to hack its own customers and undermine the security that it has put in place to protect its customers. In fact, they are asking for a key that simply doesn’t exist."

The issue of backdoors and limits to encryption technology has been a highly controversial issue in recent times, with technologists fearing that the privacy and security technology could be irrevocably damaged.

Philip Lieberman, President and CEO of Lieberman Software said: "It is well known that both the phone carriers and manufacturer of locked cell phones maintain their own set of keys within their publicly declared walled gardens to the devices they sell. This barrier to competition and their ability to select winners and losers in their app store as well as patch/improve their operating system at any time, is also the back door they have to get into any phone their wish and do as they wish at any time irrespective of a client’s wish to maintain privacy or security."

Ginsberg said: "Encryption methods have been put in place to avoid these kind of issues and the consequences they create. Further, in asking Apple to create new software for this purpose, the government is asking Apple to fundamentally weaken all iPhones. Apple is putting the correct amount of forethought into this situation, by recognising that the answer to specific cases is never to weaken security for everybody."

Cook is one of the most high profile tech leader to make such a statement on this issue. "Opposing this order is not something we take lightly. We feel we must speak up in the face of what we see as an overreach by the U.S. government," he said.

The whole debate over the relationship between major tech firms and the government has shifted dramatically in the wake of the Edward Snowden revelations about digital surveillance by the NSA in America, and GCHQ in the UK.