Twitter has apologized after an investigation found that it allowed ads to be micro-targeted at neo-Nazis, transphobes, and homophobes.
The BBC found that it was possible for brands to send ads to users who had searched for terms including "transphobic," "white supremacists," and "anti-gay." It created a generic ad saying "Happy New Year" and paid Twitter $5 to promote it via its advertising tools.
The users selected to see the ad were decided based on keywords chosen by the BBC, as a real advertiser would do with other keywords such as "sport" or "fashion" on many social media sites.
It was found that using keywords including "islamophobes," "islamaphobia", "islamophobic," and "#islamophobic" resulted in the ad potentially reaching between 92,900 and 114,000 users.
Targeting people using the term "neo-Nazi" in the UK would reach an audience of up to 81,000 people.
It was also possible to advertise to vulnerable groups.
The BBC targeted 13- to 24-year-olds using the keywords "anorexic," "bulimic," "anorexia," and "bulimia" with an estimated reach of 20,000 people.
Twitter is supposed to have restrictions in place for keyword targeting.
Its for sensitive categories including religion, race, and sex life should stop advertisers from using such keywords for promotion.
In a statement to the BBC, Twitter said that its "preventative measures include banning certain sensitive or discriminatory terms, which we update on a continuous basis.
In this instance, some of these terms were permitted for targeting purposes.
This was an error.
"We're very sorry this happened and as soon as we were made aware of the issue, we rectified it.
We continue to enforce our ads policies, including restricting the promotion of content in a wide range of areas, including inappropriate content targeting minors."
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In the past, Twitter has been criticized for not doing enough to stop the proliferation of neo-Nazis on its site, although it has taken some action against racist accounts.
It has thus far declined to remove controversial tweets from President Trump, who often amplifies and re-tweets conspiracy theories and racist individuals.
Last year, Twitter said it would implement a new system for world leaders who break its rules.
Rather than deleting offending tweets, they will carry a warning label and appear less prominently in Twitter's default search function, in users' timelines, and in the notifications tab.