The woman was the prosecution's first witness in the case against William Ruto, and she delivered a harrowing testimony to the International Criminal Court (ICC) yesterday. She was referred to only as "Witness P0536", her face pixellated and voice distorted.
But within hours of the court session, relayed live on several Kenyan television stations, viewers began speculating on her real identity on Twitter and other social media.
The ICC said it may take legal action.
"Any revelation of the identity of a witness whose identity has been protected... Amounts to an offence," the ICC's presiding judge Chile Eboe-Osuji said. "Such conducts will be investigated and the culprits will be prosecuted."
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The judge said the warning applied to "everyone inside the courtroom, in the public gallery, in Kenya, and anywhere in the world", and urged "members of the press, bloggers, social media members or participants and their web hosts... To desist from doing anything that would reveal or attempt to reveal the identity of protected witnesses."
Amnesty International said it was "deeply concerned", urging "the ICC and the Kenyan authorities to take effective measures to protect the safety and well-being of this witness and her family."
"The publication, if correct, amounts to a serious breach of an order made by ICC Judges barring the disclosure of the identity of the first witness," Amnesty's Deputy Africa Director Sarah Jackson told AFP.
The Kenyan Human Rights Commission, an independent NGO, said other witnesses could now back out of the trial.
"Now that a witness has been identified it will be difficult to assure others that they are their family members will be safe. And in Kenya, it's not just the nuclear family: there are aunts, uncles, cousins," said spokeswoman Beryl Aidi.