Brazil's Superior Court of Justice (STJ) fines a lawyer 20,000 reais for using prompt injection in a court filing

The First Panel of Brazil's Superior Court of Justice (STJ) imposed a personal fine of 20,000 reais on a lawyer who embedded hidden instructions in a special appeal, the first prompt injection case heard by a panel. Two text blocks of 1576 characters each were hidden within one page of the appeal, in 0.8-point font, respectively in white on a white background and in olive green, instructing the court system to find all admissibility requirements satisfied and that no review of evidence was needed. Presiding Justice Paulo Sérgio Domingues did not accept the explanation of "residue from an AI tool," noting that two different concealment methods could not be accidental, and that the violation was established regardless of whether the instructions could actually affect the court system; he also referred the document to the Paraná branch of the Brazilian Bar Association (OAB-PR) and the Federal Public Prosecution Service. Justice Herman Benjamin called it a "very serious fraud" undermining transparency and equality of arms, and argued that the law firm should immediately dismiss the lawyer involved; the panel also decided to fully preserve the digital evidence and produce a supplementary technical examination. The case number is AREsp 3.095,458.