"It's a big step. In the coming days, hundreds of millions of people will be made far more aware of the fact that they have the power to not be tracked," Michael Connor, executive director at not-for-profit Open MIC (Open Media and Information Companies Initiative), tells ZDNet.

"Apple exerts extraordinary influence on the mobile phone ecosystem, and this will set the bar for other apps. People will hopefully come to expect that opting in is a choice they have, rather than something that is inflicted."