The FBI has a court order demanding Apple helps unlock an iPhone belonging to the gunman behind the San Bernardino terror attack, Syed Rizwan Farook.

Farook and his wife killed 14 people in the California city last December before police fatally shot them.

Family members of some victims have backed the FBI's order.

Two groups of tech giants have now filed an amicus brief, which allows parties not directly involved in a court case, but who feel they are affected by it, to give their view.

Apple has appealed against the court order, arguing that it should not be forced to weaken the security of its own products.

Security

Since a software update released in September 2014, data on Apple devices - such as text messages and photographs - has been encrypted by default.

This prevents anyone without the owner's four-digit passcode from accessing the handset's data. If 10 incorrect attempts at the code are made, the device will automatically erase all of its data.

No-one, not even Apple, is able to access the data. But the FBI has asked the tech company to help it circumvent the security by altering Farook's iPhone.

The agency wants it to do things: first change the settings so unlimited attempts can be made at the passcode without erasing the data; and second help implement a way to rapidly try different combinations to save tapping in each one manually.

Family view

Apple has argued that the move would jeopardise the trust it has with its customers and create a backdoor for government agencies to access customer data.

Twitter, AirBnB, Ebay, LinkedIn and Reddit are among a group of 17 major online companies to have formally backed Apple in its court dispute with the FBI.

Another group have filed a separate joint amicus brief. These include Amazon, Cisco, Facebook, Google, Microsoft, Mozilla, Pinterest, Snapchat, WhatsApp and Yahoo.

Intel and AT&T have also filed separate briefs.

Salihin Kondoker, whose wife survived being shot three times in December's terror attack, has also filed a brief supporting Apple.

But family members of some other victims will jointly back the FBI's order, Reuters reported.

Analysis: Dave Lee, BBC North America Technology reporter

Apple isn't known for making it easy for journalists. A colleague once joked that staff in Apple's press office must have to replace the keys needed to spell out "no comment" on a very regular basis.

And that's because Apple didn't need to bother - its products would be talked about and reported on regardless.

But with this case, that dynamic has changed. If you're studying public relations, grab a pen.

Now, a daily email from the press team arrives in reporters' inboxes, pointing out developments, offering thoughts and bigging up coverage Apple thinks is "useful".

Today, on Apple's website, it is compiling a list of all those who support the company - quicker than we can get it from the court.

Every time I refresh there's more: 32 law professors, the Electronic Frontier Foundation, the American Civil Liberties Union.

But on the flip side, what must not be forgotten is the very powerful backing for the FBI which we expect to hear from many victims' families.

(BBC)