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Facebook Inc. (NASDAQ: FB) has disclosed more about Russian ads that ran at its site and were likely meant to affect the last election. As it passed the information to Congress, among the comments it made is that many of the ads were bought for less than $3.

According to a message from Facebook:

An estimated 10 million people in the US saw the ads. We were able to approximate the number of unique people (“reach”) who saw at least one of these ads, with our best modeling 44% of total ad impressions (number of times ads were displayed) were before the US election on November 8, 2016; 56% were after the election.

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Roughly 25% of the ads were never shown to anyone. That’s because advertising auctions are designed so that ads reach people based on relevance, and certain ads may not reach anyone as a result.

For 50% of the ads, less than $3 was spent; for 99% of the ads, less than $1,000 was spent.

No one can be sure whether the ads changed the way that even one person voted.

What the information does show is how inexpensive it can be for a person who is both clever and presumably familiar with the Facebook ad system to target groups in a manner meant to change their opinions or actions. An attempt to changing votes is among a much longer list of fake news and fake claims that can be posted on Facebook at a cost well below what most people would expect. It opens Facebook up to abuses that almost anyone can afford.

For those who want to stop fake claims from reaching people on the internet, the hurdle is very high. Facebook is only one of scores of places inaccurate information can be distributed, although it is the largest. Among all large social media sites, the number of people who can be targeted rises to the hundreds of millions. Fake news, delivered via the internet, is here to stay because in a sea of other ads it is almost impossible to detect, and it can be very cheap as well.