Uninstalling an app is no longer a sufficient method to remove it from your digital life. App developers and the companies that serve them have figured out how to identify users that have uninstalled an app and then bombard them with ads to try to get them back. Among the companies that currently offer uninstall trackers (as part of an overall toolkit for developers) are Adjust, AppsFlyer, MoEngage, Localytics and CleverTap. T-Mobile US, Spotify Technology, Yelp and Bloomberg are among the users of such tools, although the trackers are not always used to send ads.

Bloomberg reports that such tools are “a fresh reason to reassess online privacy rights and limit what companies can do with user data.” “Most tech companies are not giving people nuanced privacy choices, if they give them choices at all,” said Electronic Frontier Foundation tech policy director Jeremy Gillula.

In defense of the tools, Localytics chief executive Jude McColgan said he hasn’t seen his clients use them to send ads to former users, and MoEngage vice president, marketing and sales Ehren Maedge said it’s up to the app developers to refrain from doing so. “The dialogue is between our customers and their end users,” he said. “If they violate users’ trust, it’s not going to go well for them.”

The ability to track down users uninstalling apps relates to push notifications, a “core element” of both Apple’s and Google’s mobile operating systems. Developers use “silent push notifications to ping installed apps at regular intervals without alerting the user.” If the app doesn’t respond to the ping, it’s registered as uninstalled, which activates the uninstall tracking tools. That enables the app to advertise the app to the user, wherever he or she goes.

According to Branch Metrics chief executive Alex Austin, using silent push notifications to build advertising audiences is a violation of Apple and Google policies. “It’s just generally sketchy to track people around the Internet after they’ve opted out of using your product,” said Austin, noting that Apple and Google will likely “crack down on the practice soon.” Neither company commented.

Uninstall tracking does have its legitimate uses: “to fix bugs or otherwise refine apps without having to bother users with surveys or more intrusive tools.” But the practice still violates the user’s privacy. “As an app developer, I would expect to be able to know how many people have uninstalled an app,” said Gillula. “I would not say that, as an app developer, you have a right to know exactly who installed and uninstalled your app.”