Web User-Tracking Lawsuits Find New Tack in Pen-Register Theory

California class-action plaintiffs trying to target website user-tracking software they call a powerful surveillance tool are turning to a new theory of harm now that their claims filed under the state’s wiretap laws have run into headwinds.

Since November, a small group of plaintiffs—represented by the same attorney—have brought more than 50 class actions in California state courts against a bevy of website operators, alleging they violated state law by installing software that acts as an illegal “pen register.” Website operators targeted in the complaints include retailers Anine Bing Corp., Stitch Fix Inc., and Primer Labs Inc.

Under the California ...