What are ‘zombie cookies’? Sadly, not innocent baked goods shaped like Halloween creatures, but a kind of tracking cookie that lives on your computer and rises from the dead even after being deleted.

Zombie cookies came to light in Julia Angwin’s investigation into an online advertising company’s use of a hidden undeletable number produced by Verizon to monitor customers’ web surfing on tablets and smartphones. The company, called Turn, uses Verizon’s number to recreate tracking cookies even after a user deletes it, which Editor-in-Chief Steve Engelberg deems a “sneaky” practice in his discussion with Angwin on the podcast.

After respawning the dead cookie, Turn can continue to track a user’s Web browsing habits and use that information to attract advertisers to online auctions of user profiles. The highest bidder instantly serves an ad on the user’s web page as it loads. Turn is relied on by many companies, including Google, Yahoo and Facebook.

“[Turn] said they don’t believe that clearing cookies is any sort of sign of user intent to want to protect their privacy, and that it was actually a service to recreate the cookie for that person,” Angwin says.

In response to ProPublica’s report and the subsequent outrage online from the tech community, Turn reevaluated the practice and decided to stop using zombie cookies.

This doesn’t mean that other companies won’t use Verizon’s undeletable tracking number, particularly since there are no federal online privacy laws that specifically prevent the practice. Engelberg describes Internet privacy as the “wild west” and quotes Internet whistleblower Edward Snowden, who said, “The internet is a television that watches you.”

For Verizon, selling data about their subscribers appears to be a profitable business – profiles are built in an “anonymized fashion” without name, address, and other personally identifiable information, but this doesn’t mean the average tech whizz can’t hack private info. Angwin questions whether the mobile giant will continue to track its customers with an undeletable number now that Turn has abused the practice and other companies like AT&T have stopped because of the privacy implications.

In fact, in today’s New York Times, a Verizon official is quoted saying that the flap over zombie cookies is causing the telecom giant to consider offering customers a way to opt out of having the tracking number attached to their devices.

Catch this podcast on iTunes, SoundCloud or Stitcher, and read Angwin's full investigation here.