In a statement, Apple emphasized it will continue to fight unjustified legal demands for personal information and keep customers informed about them.
But in this instance, Apple said it was constrained by a nondisclosure order signed by a federal magistrate judge and said it had no information about the nature of the investigation.
“It would have been virtually impossible for Apple to understand the intent of the desired information without digging through users’ accounts," the Cupertino, California, company said. “Consistent with the request, Apple limited the information it provided to account subscriber information and did not provide any content such as emails or pictures."
Apple also believes other technology companies may have been confronted with similar legal demands, based on the broad nature of the request it received for “customer or subscriber account information” spanning 73 phone numbers and 36 email addresses.
It remains unclear how many other companies may have been swept up in the Trump administration's attempt to track down leakers.
In a statement, Microsoft acknowledged receiving at least one subpoena in 2017 related to a personal email account. It said it notified the customer after the gag order expired and learned that the person was a congressional staff member. “We will continue to aggressively seek reform that imposes reasonable limits on government secrecy in cases like this,” the company said.
Privacy experts were more troubled by the U.S. laws that allowed the Justice Department to secretly obtain the subpoenas and then keep them under wraps for years than by Apple's limited compliance with the demands.
The subpoenas represent a “a quintessential example of government abuse” that ensnared Apple, said Alan Butler, executive director of the Electronic Privacy Information Center.
“It’s very difficult to challenge these types of subpoenas, but it’s not impossible,” Butler said. “And if there ever was one worth challenging, it might have been these.”
Apple's response to the subpoena doesn't necessarily contradict its stance on the sanctity of personal privacy, said Cindy Cohn, executive director for the Electronic Frontier Foundation, a digital rights group. That's because Apple privacy commitments mostly revolve around shielding its customers from online surveillance.
She thinks the bigger issue is why U.S. law allows a grand jury to issue a subpoena and then block Apple from alerting the affected people.
“The overall secrecy of this is troubling, especially since it appears to have all been a politically motivated investigation,” Cohn said.
Apple has a history of fighting legal requests, most notably in 2016 when the Justice Department sought to force Apple to unlock the iPhone owned by one of the killers in a mass shooting in San Bernardino, California.
Apple refused to cooperate, contending it would open a digital backdoor that would pose threats to the security and privacy of all iPhone users. The legal showdown ended when the FBI hired another firm to unlock the iPhone connected to the shooting.
“Apple really put its money where its mouth is that time,” Butler said.