User privacy is a product feature Apple has been heavily advertising recently and it’s been making sure customers know their data is safe… but that doesn’t mean advertisers and retailers won’t still be able to track some Apple device users. For example, even if you use an iOS 8 privacy feature called MAC address spoofing that was designed to stop advertisers from tracking you, you still aren’t necessarily safe from marketers’ prying eyes.

A MAC address is a unique identifier associated with a device that has Wi-Fi connectivity, including iPhones or any other smartphone, and can be used by third parties to track users whose devices are constantly looking for a Wi-Fi connection.

According to a report from Airtight Networks, a company that deals with MAC-based location tracking, iOS 8 users need to have certain settings in place to make sure MAC spoofing works, including turning off location services and cellular data, which may not be convenient for the user.

Even with these settings switched off when MAC spoofing is enabled, the company found that spoofing works in sleep mode only, but not once the screen of the device is turned on.

The MAC spoofing feature will be available to iPhone 6 users, but not on older devices (such as iPhone 5 or older, or iPad minis).

Finally, companies could still find ways to find out the real MAC address associated with a device even when MAC spoofing is in place.

“It’s easy to weed out the random MACs from real MACs because they use special signatures,” Airtight’s vice president Hemant Chaskar told The Verge. “So if you want to sanitize the sample set before doing your big data analysis, that is possible.”