REUTERS

Apple Inc (AAPL.O) Chief Executive Tim Cook on Friday told a court that threatsto iPhone security and privacy required tight control of the App Store, which "Fortnite" game maker Epic Games says is a monopoly that Apple illegally abuses.

The testimony constitutes Cook's most extensive public remarks on the App Store, which anchors Apple's $53.8 billion services business, at a time when the company that once urged the world to 'think different' is criticized as too big and too powerful.

Epic has waged a public relations and legal campaign, parodying Apple's iconic "1984" commercial and arguing that it acts anticompetitively by only allowing approved apps on the world's 1 billion iPhones and forcing developers to use Apple's in-app payment system which charges sales commissions of up to 30%. 

Cook under questioning said he had higher concerns about the phone than Mac computers. "You have a phone in your pocket most of the time and you want instant service. We felt both the use cases and the threat profile would eventually be much greater because of the number of iPhones on the market."

Cook said an Apple document produced in the trial and showing a 78% profit margin for the App Store did not account for several costs and was meant to show trends, not a true bottom line.

Epic has argued that the Mac is very safe without Apple's App Store review and that most of the privacy and security benefits come from the operating system, not App Store rules.

The maker of "Fortnite," which pits players against in each other in an animated "Battle Royale" fight to the last survivor, is led by CEO Tim Sweeney, who has reveled in the public opportunity to take on Apple.