As we noted a few weeks ago, Verizon and AT&T recently began utilizing a controversial new snoopvertising method that involves meddling with user traffic to insert a unique identifier traffic header, or X-UIDH. This header is then read by marketing partners to track your behavior around the Internet, which Verizon and AT&T then hope to sell to marketers and other third parties. In addition to the fact they‘re modifying user traffic, these headers can also be read by third parties — even if customers opt out from carrier-specific programs.