United States senator Maggie Hassan is pressing major data brokers after an investigation by The Markup / CalMatters and co-published by WIRED found at least 35 firms hid opt-out information from search results, making it harder for people to take control of their own data and safeguard their privacy online.

Hassan, the top Democrat on the Joint Economic Committee, put five of the top firms—IQVIA Digital, Comscore, Telesign Corporation, 6sense Insights, and Findem— on notice Wednesday , demanding that each explain why code on their sites appears designed to frustrate deletion requests.

None of the companies immediately responded to WIRED’s request for comment. None previously responded to requests for comment during the investigation.

California law requires brokers to provide a

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