Within a week of Facebook's declaration of war on ad blockers, it was clear the social network couldn't win.

First, AdBlock Plus, the most popular desktop ad blocking service, spotted parts of Facebook’s code that allowed it to discern ads despite Facebook's attempt to hide such indicators.

Ben Williams, the ad blocker's outspoken spokesman, expected the discovery to trigger a game of cat and mouse between Facebook and the open source software community.

The company, along with a handful of other ad blockers, did continue in a back-and-forth with Facebook's engineers for a time.

But the game didn't last long. Facebook's plans had a fatal flaw, at least in theory: its strategy towards shutting down ad blockers depends on obscuring the difference between user posts and ads; but the company is also required to clearly mark ads to users by Federal Trade Commission rules.

Developers soon seized on this contradiction with software that could look for "sponsored" markers on the front end and block those posts accordingly.

"As long as [Facebook] has to let people know that an ad is an ad — and I see no reason for that to change — people can always use ad blocking," says Roy Rosenfeld, CEO of charity-focused ad blocker Stands, who programmed a workaround the weekend after Facebook's announcement.

Arvind Narayanan, a computer science professor at Princeton University, and graduate student Grant Storey came to the same conclusion just hours after AdBlock Plus's update. To prove it, they developed a browser extension that marks, but doesn't block, ads in the News Feed.

Narayanan's extension in action. While Facebook claims workarounds like these tend to mistakenly lump in user posts, an anecdotal look at 200 or so posts revealed no mislabeling. Image: screenshot, Facebook

"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," he wrote in an accompanying blog post.

Indeed, it doesn't take too much reasoning to arrive at this logical endpoint. So why all the fanfare on Facebook's part?

The company wouldn't comment on the record, so we don't know for sure.

Facebook may believe that while it can't completely shut out ad blockers, it could conceivably obscure ads to the point where blocking them costs more overhead than it's worth to ad blockers.

Williams thinks that this tack can only go so far before it starts becoming deceptive to Facebook's actual human users, which would no doubt draw the FTC's suspicion.

"If this practice is taken further, it could be very deceptive for people who cannot see the screen as Facebook intended it," Williams said. "For instance, those who use assistive technology like screen readers, people with poor or no eyesight for example, might not be able to tell the difference between ads and organic content."

Facebook could also follow the lead of some publishers and lock out ad blocker users until they turn them off. That seems unlikely though, given the potential harm to the user growth metric coveted by Wall Street.

It's also possible the move was meant as more of a threatening statement than a surefire fix. While many of Facebook's peers quietly pay AdBlock Plus to whitelist their ads, the social network is signaling that it won't bow to such pressure.

"Behind the scenes is this tussle over the fact that Google, Microsoft, Yahoo, Outbrain, Taboola — all these guys — have paid to be on the ostensible whitelist for Eyeo, [the developer behind AdBlock Plus] and Facebook is resisting," says David Carroll, a professor of media design at the New School who has studied Eyeo's business model in depth.

"This is as much Facebook telling AdBlock Plus that they're not going to pay for its so-called 'extortion fees,'" he continued.

Eyeo's so-called "acceptable ads program" has been criticized by consumer advocates — including the above-mentioned professor — and industry trade groups for its lack of transparency. It's not entirely clear what criteria a website must meet to land a free spot, and the German software developer's plans to form a third-party nonprofit panel to oversee have yet to materialize.

The Interactive Advertising Bureau in particular has not been shy about blasting the program, likening the ad blocker, on various occasions, to "highway robbery," "terrorists" and "inner city crack dealers."

Based on information Eyeo shared with him in private, Carroll says the admission fee applies to all websites with traffic above a certain threshold. Less trafficked websites with ads that meet the conditions are accepted for free if they apply.

Facebook gets less than a fifth of its ad revenue from desktop posts, and many of the same demographics that use ad blockers are probably more likely to visit on their smartphones, where ad blocking hasn't been widely adopted. So Facebook's financial stake in this fight is relatively small.

But the company does have important business relationships with publishers and advertisers, who might take comfort in the appearance of Facebook putting its foot down in this manner.

The company is by far the biggest business yet to enter the ring in a larger battle between ad blockers and the advertising and media industries. Just the act of it throwing its massive weight into the fight might be a symbolic victory, if nothing else.

Facebook may have also seen the opportunity for some good PR in updating its ad preferences panel to give users more control over the types of ads they see.

Carroll argues this gesture is largely meaningless, though, since Facebook refuses to cede users the option of bowing out of its extensive web of third-party website cookies and trackers that follow users around the internet.

"It's not just about showing the ads, it's about doing the market research on us collectively," he says. "The ad is really a camouflage for surveillance, and I think that's really the bigger story."

Facebook has made it much more clear what it knows about you and how you can stop seeing ads based on that information, but it still doesn't let you stop it from collecting that data.

Some of these trackers are even let through AdBlockPlus's wall by default, though services like Disconnect and Ghostery (though it has its own conflicts of interest) exist to block them.

Whatever Facebook's motivations, it hasn't budged on its hardline stance, and ad blocker workarounds have been met with an uncharacteristically aggressive response from Facebook's PR department. The social network clearly intends to keep up the fight.