Twitter has apologised for allowing adverts to be micro-targeted at certain users such as neo-Nazis, homophobes and other hate groups.
Twitter allows ads to be directed at users who have posted about or searched for specific topics.
But the firm has now said it is sorry for failing to exclude discriminatory terms.
Anti-hate charities had raised concerns that the US tech company’s advertising platform could have been used to spread intolerance.
Like many social media companies, Twitter creates detailed profiles of its users by collecting data on the things they post, like, watch and share.
Advertisers can take advantage of this by using its tools to select their campaign audience from a list of characteristics, for example “parents of teenagers”, or “amateur photographers”.
They can also control who sees their message by using keywords.
Twitter gives the advertiser an estimate for how many users are likely to qualify as a result.