According to estimates arrived at by computer engineers and software developers, Apple Inc. would have to spend $101,000 to assist the FBI in hacking a terrorist's iPhone. But that's not all. In order to not let this hack from going out into the open, the tech giant has to spend millions of dollars more.

This was revealed by Apple in court documents filed on Thursday, as to what the company needs to do to hack one of its iPhones. Previously, Apple was ordered by a federal magistrate-judge to design a back-door hack that will help the FBI to break into a San Bernardino shooter's iPhone 5C.

Although the computer giant has already estimated the cost of hacking, it is not willing to do the bidding of the court without a fight. Apple also indicated that a new version of its OS will have to be designed. It was called "GovtOS" by one of its staff.

"All told, I would estimate that the process of designing, creating, validating, deploying GovtOS would take two to four weeks," said Erik Neuenschwander, manager of user privacy at Apple, according to the papers filed court.

Neuenschwander added that it would take "six to ten Apple engineers and employees dedicating a very substantial portion of their time."

Tim Cook, Apple's CEO is refusing to give in to the demands of the FBI.

"The government is asking Apple to hack our own users and undermine decades of security advancements that protect our customers," said Cook in a public letter.

"The same engineers who built strong encryption into the iPhone to protect our users would, ironically, be ordered to weaken those protections and make our users less safe," he added.

But the FBI is equally adamant. The spy agency has previously been critical of the tech giant's encryption tactics and argued that these will impede their investigations. It has been lobbying with congress to pass a law that requires Apple to build OS backdoors.