One privacy advocate tied Yahoo's announcement to the Friday launch of Windows 8. "Hunch: Yahoo walked back its Do Not Track commitment today because of the Win8/IE10 launch," said on Twitter.

Mayer is a graduate student in computer science and law at Stanford University, and one of two researchers at the school who created the HTTP header implementation that signals a user's DNT preference.

Microsoft debuted IE10 on Oct. 26 as part of Windows 8. A version of the browser for the will reach beta -- Microsoft calls that a "preview" -- in mid-November. IE10 on Windows 7 will also have the DNT option enabled by default.

"At least Yahoo is honest about why it's ignoring IE10 Do Not Track," noted Mayer, , as he quoted the company's claim that the privacy feature, if turned on, "makes it hard to deliver on our value proposition."

Also on Friday, Microsoft's head counsel, Brad Smith, blogged about DNT. Because his comments were based on an Oct. 23 keynote speech at an international conference of data protection and privacy officials, he did not address Yahoo's move.