Sometimes the stories are political; other times they’re too intriguing not to share, with tempting pieces of celebrity news. “That can’t possibly be true,” we say when seeing a headline that, say, Hillary Clinton and Yoko Ono have been lovers for years. You click, and advertisements load on the site, benefiting its creators… and the ad networks that profit.

Google and Facebook have recently promised to ban “fake news” from their ad placement and tracking services, but the problem is that banning entire sites is a subjective and tedious process, and turns into an internet-wide game of Whac-A-Mole that never lets up.

Should “parody” sites that don’t clearly label themselves be banned from entire ad networks? Should it be up to the companies that run ad networks, or any of the multiple middlemen who help fill all of that inventory, or should advertisers choose what kind of sites they don’t want their brands to appear on, and block categories and sites accordingly?

A representative for Fiat Chrysler explained to the Wall Street Journal that the problem is that while some categories like adult content can be blocked broadly, sites that are out to misinform people have to be blocked manually. There is no truth filter.

To an extent, it doesn’t really matter what brands want: Banned publishers can re-appear under new names, and automated bidding and approval processes mean that campaigns go online without a human reviewing them.

“We’re in the process of implementing the new policy and these early stages have demanded increased human review,” Google said in a statement, but humans are expensive and slow.

Another problem is that ad networks don’t want to be in the truth-arbiting business. The Los Angeles Times traced an untrue but attention-grabbing story about actor Tom Hanks endorsing Donald Trump for president to multiple sites that were part of common ad networks.

Yet one online ad executive questioned whether his company should be in the role of truth squad. Is it financially wise to kick good sites off the network because they report something wrong by mistake? “I like to do things for the net good of society, but the deeper I look into this, it’s a more thorny situation,” he said of the fake-news situation.

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