Facebook can’t win the war it started on ad blockers last week.

So say Princeton assistant professor Arvind Narayanan and undergraduate Grant Storey, who have created an experimental ad “highlighter” for the Chrome browser to prove it. When you have Facebook Ad Highlighter installed, ads in the News Feed are grayed out and written over with the words “THIS IS AN AD.”

Facebook announced that it was taking measures to prevent ad blockers from working on Tuesday last week. On Thursday the largest ad blocker out there, Adblock Plus, informed users of a simple tweak to their settings that would defeat Facebook’s blocker blockade.

Princeton researchers say Facebook can’t prevent their experimental add-on for the Chrome browser graying out ads in your News Feed.

We’re still waiting for Facebook to fire back, as the executive leading its ad technology has promised it will. But Narayanan argues in a blog post introducing his ad highlighter that Facebook simply can’t win.

The ad blockers in use today work by looking at the HTML code that tells your Web browser how to render a page and where to get the images and other files embedded into it. Facebook’s initial move against ad blockers removed clues in its HTML that gave away which parts of a page were ad content.

The Princeton duo’s ad highlighter works differently. It looks at the parts of the Web page that are visible to humans. Facebook Ad Highlighter simply looks for and blocks any posts with a giveaway “Sponsored” tag. It appears to be quite effective. Facebook must clearly label ads to stay within Federal Trade Commission rules on transparency and its own commitments to its users.

Narayanan concludes in his post that Facebook’s anti-ad-blocking campaign is doomed, at least if it continues in the current vein of acting as if the social network can somehow neutralize ad blockers completely.

“This is a simple proof of concept, but the detection method could easily be made much more robust without incurring a performance penalty,” he writes. “All of this must be utterly obvious to the smart engineers at Facebook, so the whole ‘unblockable ads’ PR push seems likely to be a big bluff.”

Narayanan suggests that to reach the hundreds of millions of people who use ad blockers, Facebook should focus on making its ads less objectionable to them.

(Read more: “Facebook Has Nuked Ad Blockers, for Now,” The Ad Blocking Kingpin Reshaping the Web as He Prefers It,” “Are Ad Blockers Needed to Stay Safe Online?,” “Facebook Blocks Ad Blockers, but It Strives to Make Ads More Relevant,” “The Rise of the Anti-Ad Blockers.”)