Jim Brock, Privacy Choice's CEO and founder, said independent tests such as the one from Carnegie Mellon are very valuable, even if they are subjective, and Privacy Choice will take the findings into account.

However, Privacy Choice's principal blocking service for consumers is TrackerBlock, which the Carnegie Mellon researchers didn't include in the study, and not PrivacyMark, he said via e-mail.

In addition, internal surveys at reveal that more than 75 percent of PrivacyMark users understand what the service does and would recommend it to a friend, he said.

The Digital Advertising Alliance, Mozilla and Adblock Plus didn't immediately respond to a request for comment.

The IDG News Service