Sigurdur Ingi Thordarson (Icelandic: Sigurður Ingi Þórðarson) (born 1992), commonly known as Siggi hakkari ("Siggi the Hacker"), is an Icelandic convicted criminal and FBI informant against WikiLeaks. He is known for information leaks, multiple cases of fraud and embezzlement, sexual solicitation of minors and adults. He has multiple convictions for sexual offences. In June 2021, in an interview with Icelandic newspaper Stundin, Thordarson recanted some of the previous accusations he had made against Julian Assange, which Stundin said were used in the American indictment against Assange.