Privacy groups are warning more than 100 million people about their cell phone carriers.
Verizon and AT&T are tracking online activity with so-called "supercookies" that monitor and catalog the websites and serve to increase advertising revenue.
"These programs have been in place for a couple years now and really are only coming into light at this point, so it's a little bit disconcerting ultimately that it's been going on for a long time now," CNET editor Tim Stevens said on "CBS This Morning."
The companies create unique ID numbers that tag every piece of web traffic generated by the user. Simply, the phone carriers know what websites you're visiting even if you're surfing under the veil of a privacy mode.
But that's not the biggest problem.
"Anyone on the web can look at these identifiers and do a reverse look-up and figure out who you are and where you've been going across the web," Stevens said. "Especially if you're, for example, sitting in a coffee shop and you're surfing the web on an unencrypted connection. At that point, these IDs are kind of floating around in the air and anyone in the coffee shop could be monitoring all the traffic and looking at all those IDs and again seeing what sites you're visiting even if they're not looking at your computer."
While these types of cookies are raising concern, conventional trackers can and have been used for good. Traditional cookies store information for websites you visit often and can save you time by storing log-in information.
While there are options to prevent "supercookie" tracking, it's not easy to do.
"Verizon does offer an opt-out, but the problem is while it'll opt you out of their advertising program, it doesn't actually stop them from putting this ID onto your information, which is a problem," Stevens said. "AT&T's system, they said if you opt out, they will stop putting that ID on there, but ultimately there's no easy way to flip it off."
Stevens pointed out that Apple also has similar tracking techniques for advertising, but those can easily be disabled in a user's privacy settings.