And once configured, the tools didn't clearly communicate to users what they were doing, particularly when they blocked specific content and functionality in websites users were visiting.

The design of the user interfaces also contributed to the users' confusion and inability to properly use the tools, according to the study.

"Our results suggest that the current approach for advertising industry self-regulation through opt-out mechanisms is fundamentally flawed," the researchers wrote.

The tools evaluated by the study are DAA Consumer Choice from the Digital Advertising Alliance; Global Opt-Out and Ghostery 2.5.3, both from Evidon; Privacy Choice's PrivacyMark; TACO 4.0 from Abine; Adblock Plus 1.3.9; Mozilla Firefox 5's privacy panel; and Microsoft IE9's privacy controls and Tracking Protection mechanism.

Rob Shavell, co-founder of , agrees with the researchers' general conclusion.