Ad blockers out-flank Facebook

Ad blockers on Thursday said they foiled a move by Facebook to sidestep software used to stop marketing messages at social network pages visited on desktop computers.

Adblock Plus announced that it is updating its free software with a new filter that will thwart Facebook's effort -- for now.

"We promised that the open source community would have a solution very soon, and, frankly, they've beaten even our own expectations," Adblock Plus communications manager Ben Williams said in an online post.

"It's very possible that Facebook will write some code that will render the filter useless -- at any time."

He warned users not to be surprised if the maneuvering turns into an ongoing duel, with each side countering moves by the other.

"This sort of back-and-forth battle between the open source ad-blocking community and circumventers has been going on since ad blocking was invented," Williams said.

"But for this round of the cat-and-mouse contest, it looks like the mouse won."

An update to Facebook's advertising platform on Tuesday came with assurances that the leading social network understands how annoying ads can be, announcing enhanced tools for controlling the kinds of ads shown to users.

"As we offer people more powerful controls, we'll also begin showing ads on Facebook desktop for people who currently use ad-blocking software," vice president of ads and business platform Andrew Bosworth said in a blog post.

Although ad-blocking software typically does not work on mobile devices -- which account for most visits to the social network -- it is estimated to stymie billions of dollars' worth of ads annually.

Advertising pays for online services people have grown accustomed to accessing free.

Facebook ads on desktops are being made to look so much like natural content that they get by ad blockers.

As a counter-balance, Facebook made it easier to use its ad-preferences tools, which let people remove topics that don't interest them and stop advertising from businesses or organizations that have added them to customer lists.

In its latest quarterly report, Facebook said it took in $6.2 billion in advertising revenue, accounting for the overwhelming majority of its income. Some 84 percent of ad revenues came from messages delivered to mobile devices.