Former Apple engineer says the button on iPhones asking apps not to track you is a 'dud' that gives users a 'false sense of privacy'

• In April, Apple rolled out a privacy feature that allows users to ask apps not to track their data.
• A new study found popular iPhone apps are still collecting user data - even if they're asked not to.
• Apple claims "what happens on your iPhone, stays on your iPhone." A former employee says argues that's not the case.

Johnny Lin, a former Apple engineer and co-founder of the software company Lockdown Privacy says Apple's "Ask App Not To Track" button is a "dud" that gives users "a false sense of privacy," according to a Washington Post report.

Even if users request apps not to collect their activity across other companies' apps and websites, popular iPhone apps like Subway Surfers still collect personal data, a new study by Lockdown Privacy determined.

"We found that App Tracking Transparency made no difference in the total number of active third-party trackers," the study says. "We further confirmed that detailed personal or device data was being sent to trackers in almost all cases."

Sybo, the company that makes Subway Surfers, told The Washington Post that "in order for the game to function properly, some data is communicated to Ad Networks," but did not explain why detailed personal information was required. "As a company, we do not track users for advertising purposes without their consent," Sybo added.

"When the user selects 'Ask App Not to Track,' the app is informed that the user would not like to be tracked by any means, and all developers - including Apple - are strictly required to comply with the user's choice," an Apple spokesperson told Insider. "If we discover that a developer is not honoring the user's choice, we will work with the developer to address the issue, or they will be removed from the App Store."

Lockdown Privacy's findings are in stark contrast to Apple's privacy-focused marketing campaigns, highlighted in advertisements like this giant billboard in Las Vegas claiming "What happens on your iPhone, stays on your iPhone."

Critics of the ad have called it misleading. Much of what users do on their iPhones and the data they generate doesn't stay on their devices. iPhones routinely send some data to wireless carriers, websites, app developers - and to Apple's own servers and services.

Apple recently announced plans to update its iOS software to scan iPhones for child sexual abuse imagery, but has since delayed the plan after criticism from privacy advocates.