In what should be no surprise, the FBI has said that it will not disclose the way in which it unlocked the iPhone used by one of the shooters in last year's San Bernardino killing spree.

The FBI said that it will not disclose the method because it did not have the details from the outside source.

Amy Hess, the FBI's executive assistant director for science and technology, said: "The FBI purchased the method from an outside party so that we could unlock the San Bernardino device. We did not, however, purchase the rights to technical details about how the method functions, or the nature and extent of any vulnerability upon which the method may rely in order to operate."

The agency has not disclosed what it found on the phone, but it has reiterated that it was important for its investigation in a major national security case.

Activists have said that the FBI should disclose the method under the policy outlined by the US administration, known as the Vulnerabilities Equities Process. That policy is in place to allow for the patching of software and hardware weaknesses to protect against hackers.

Hess said the FBI normally "must maintain confidentiality" about its actions on vulnerabilities but that it chose to make the matter public due to "the extraordinary nature of this particular case, the intense public interest in it, and the fact that the FBI already has disclosed publicly the existence of the method."

Source: Security Week