The Federal Communications Commission is reviewing whether Verizon's use of a tracking "supercookie" runs up against its consumer privacy and data security rules.
FCC Chairman Tom Wheeler disclosed the review in a letter sent to lawmakers late last month but made public Thursday.
The tool Verizon employs uses a unique identifier that follows wireless subscribers’ Internet browsing in order to allow websites to identify the user. The tool, which it calls a unique identifier header, helps Verizon target certain ads to specific demographics.
Civil liberties advocates had raised concerns about the tracking tool, warning that third parties could exploit it, even when customers had opted out of the Verizon ad program.
Following backlash by the public and some lawmakers earlier this year, Verizon recently completed an update to allow subscribers to completely opt out of the tracking.
Democratic Sens. Bill Nelson (Fla.), Richard Blumenthal (Conn.) and Ed Markey (Mass.) are considering legislation on the issue. And in February, they called on both the FCC and the Federal Trade Commission to see if Verizon's supercookie violated any of their regulations.
Wheeler noted telecommunications companies are required to protect sensitive user information under the terms of the Communications Act. The commission routinely evaluates its rules as new technologies emerge, he said. But the commission has taken a specific interest in supercookies.
"We are looking specifically into carriers' injection of header information and the collection and use of information about their subscribers' Internet activity," Wheeler wrote. "As you suggest, we will be considering the extent to which our rules and policies relating to consumer privacy, data security and transparency may be implicated."
The letter was sent March 23. The FCC had no updates to offer as of Thursday.