Apple Inc. is offering cybersecurity researchers up to $1 million US to detect flaws in iPhones, the largest reward offered by a company to defend against hackers.

The prize​​​​​ comes at a time of rising concern about governments breaking into the mobile devices of dissidents, journalists and human rights advocates.

Unlike other technology providers, Apple previously offered rewards only to invited researchers who tried to find flaws in its phones and cloud backups.

At the annual Black Hat security conference in Las Vegas on Thursday, the company said it would open the process to all researchers, add Mac software and other targets, and offer a range of rewards, called "bounties," for the most significant findings.

The $1 million US prize would apply only to remote access to the iPhone kernel without any action from the phone's user. Apple's previous highest bounty was $200,000 for friendly reports of bugs that can then be fixed with software updates and not leave them exposed to criminals or spies.

Government contractors and brokers have paid as much as $2 million US for the most effective hacking techniques to obtain information from devices. Apple's new bounties, however, are in the same range as some published prices from contractors.

Apple is taking other steps to make research easier, including offering a modified phone that has some security measures disabled.

A number of private companies, such as Israel's NSO Group, sell hacking capabilities to governments.

"NSO Group develops technology that is licensed to intelligence and law enforcement agencies for the sole purpose of preventing and investigating terror and crime," the company said in a statement. "It is not a tool to target journalists for doing their job or to silence critics."