Apple on Wednesday invited security researchers to apply to receive modified iPhones designed to help them hunt for flaws in the company's mobile operating system.

The phones will let the researchers run any programs on them and give those programs any access to the data on the device, making it easier for outside security experts to probe iOS software.

Apple had promised the initiative a year ago, and the long lead time frustrated some security experts as serious flaws have continued to be discovered.

Specialists have long argued that the opacity of Apple's devices has not made them more secure than phones running Android and other software - it just made analysis harder.

Those concerns ramped up after Apple sued a company that offered an emulation of iOS on copyright infringement grounds. That case against Corellium is still pending.

Apple has some of the top security talent in the private sector, but its devices have been targeted effectively by national intelligence agencies and some arms contractors.

Smaller companies sell police departments gear that can unlock many devices and download their contents, though those tools are not foolproof.

Apple executives speaking to Reuters before the announcement said they would pick an unannounced number of established researchers to get the first batch of modified phones.

In return, the researchers must pledge to notify Apple of any security holes they find and negotiate time for the company to confirm the issue and release a patch for users to install.

The company said it would also make senior engineers available to discuss issues that arise with the researchers, another step toward increased openness and away from its past secretive policies.