Facebook's first conservative announcement since the election was called used local targeting tools to attack Jeremy Corbyn in the main marginal district of Milton Keynes.
The ad uses old images to claim that Corbyn had "harsh words to Milton Keynes voters."
It was designed to be seen only by people in Milton Keynes, home to two major marginal chairs disputed between Labor and Conservatives.
Labor said the images were taken out of context, calling them "disappointing."
For the first time on October 31, the ad has received up to 34,000 views at a cost of about £ 300, potentially reaching 15% of Milton Keynes's population.
The three versions of the ad are aimed predominantly at 25-34 year olds, mostly women, prompting digital advertising experts to warn that it could be used to "demotivate young Labor voters."
The ad is linked to an article in Spectator magazine with the headline "Jeremy Corbyn Condemns the People of Milton Keynes".
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Refers to a speech by Corbyn at Milton Keynes in 2010.
In his speech following that year's general election, Corbyn referred to the defeat of Labor candidate Phyllis Starkey, saying: "I condemn the people of Milton Keynes for the mistakes they made in the May elections, but they will have a chance to correct your mistake hopefully in the very near future. "
Ad was predominantly 25-34 years old
In the speech, Corbyn also says that "Battersea's electorate made such a big mistake" after voting in his Labor parliament.
Hannah O'Neill, Labor candidate in Milton Keynes South, said it was "disappointing" that conservatives were "using images from nine years ago … this clearly shows the pity of Westminster's loss by his colleague Phyllis Starkey
"I hope that in the coming weeks the debate will go to politics and these political maneuvers will stop."
Other Facebook targeting information viewed by Sky News shows that it uses social networking's age and local targeting tools to target "people 18 and older" whose "primary location is Milton Keynes."
Under the Radar: Election 2019
Digital advertising experts said this kind of micro-targeting shows the sophistication of the digital campaign.
"The ads seem designed to demotivate younger Labor voters, instead of casting votes for conservatives," said Sam Jeffers, founder of the nonprofit WhoTargetsMe.
"It's an early sign of how much more complex campaigns are than simply thinking about what pleases Workington Man," said the older white man in the north as the conservative target voter.
Tim Rigby, a Milton Keynes resident who saw the ad, said he found the approach worrying.
"To be honest, it's not the target that matters to me as much as the fact that the headline of the article is so deliberately misleading – not to mention it was 2011 and was obviously posted directly after Corbyn's visit," he told Sky News. .
Rigby, who also saw Labor ads in his Facebook feed, said he was concerned about transparency.
"Because they can be so personally directed, it can be difficult to know who is seeing what, which can make it difficult to hold the party accountable."
Conservative Party announcement attacks Jeremy Corbyn, using comments he made nine years ago
Carl Miller, co-founder of the Social Media Analysis Center, said there was a risk that such ads could cause division.
"Advertisers have long understood that the closest problems people have are the ones they really care about," he said.
"Although the history of this election is one of national polarization, there are thousands of local polarizations happening side by side."
Conservatives did not respond to a request for comment.
The speech in which Corbyn commented was reported January 3 by Twitter user TheGolem.
A day later, he was picked by the anonymous gossip columnist for The Spectator magazine, who published a blog post using the title "Jeremy Corbyn Condemns the People of Milton Keynes".
Right-wing blog Guido Fawkes published a post about the images on October 31, before Corbyn's visit to Milton Keynes.
Milton Keynes has been involved in another controversy over locally targeted ads on Facebook, as the government has been accused of using public funds to target voters in major marginal constituencies.
The Huffington Post reported today that ads promoting the government's £ 3.6 billion Towns Fund have appeared in 17 cities, including several with battlefield seats – such as Milton Keynes.
Labor Representative Ian Lucas wrote to Cabinet Minister Michael Gove calling the use of public funds "outrageous."
He added: "These marginal constituencies seem to have been selected on a political basis."
A government spokesman told the Huffington Post that the "posts were published before the election and the parliament has not yet been dissolved.
"All selected cities were chosen according to the same selection methodology, including deprivation analysis, Brexit exposure, productivity, economic resilience and investment opportunities."
Under Radar, there is a Sky News project to investigate online political activity throughout the election, from ads targeted to misinformation.