Existing blockers scour a webpage's source code for signs that they are ads, but those can easily be disguised by anti ad-blocking sites. Narayanan's team designed Perceptual to ignore hidden HTML markup (or tags) and look instead at the actual content (i.e., words and pictures on the page).

Narayanan and Princeton undergraduate Grant Storey already released a Facebook-specific version of its ad-highlighting extension in November, after the social network announced it would make its ads look like regular posts to thwart blockers. That extension already supports several thousand users, said Narayanan. Today's release extends that ability to the rest of the Internet, targeting AdChoice displays.

"We don't claim to have created an undefeatable ad blocker, but we identify an evolving combination of technical and legal factors that will determine the "end game" of the arms race," Narayanan wrote in a blog post. Out of the 50 known anti-ad-blocking sites his team tested, the perceptual ad blocker was able to highlight ads on all of them without being detected.

Because there are laws around ads being labeled clearly so as not to mislead consumers, there will always be some form of identifier around sponsored content that the perceptual ad blocker is supposed to be able to suss out. This means it has a very good chance of continued success, that is, unless companies find a way to serve you ads without you knowing at all.