"DNT was really designed to prevent this sort of user-browser-advertiser war ... but I know most of the browser makers are getting increasingly skeptical about how ad networks are going to honor the signal," said Brookman. "Escalated warfare may be inevitable."
Microsoft did not respond to a request for comment on Yahoo's announcement.
Gregg Keizer covers Microsoft, security issues, Apple, Web browsers and general technology breaking news for Computerworld. Follow Gregg on Twitter at @gkeizer, on Google+ or subscribe to Gregg's RSS feed. His email address is firstname.lastname@example.org.
Read more about privacy in Computerworld's Privacy Topic Center.