US lawyers are warning their clients that AI chatbots can be used against them in court, following a federal judge's ruling that the former CEO of a bankrupt financial services company could not shield his AI chats from securities fraud charges against him. The warning comes after Bradley Heppner was charged with securities and wire fraud and had used chatbot Claude to prepare reports about his case for his defense lawyers. The court ruling was seen as an early test in the AI chatbot era for "bedrock legal protections" regarding attorney-client communications and materials prepared for litigation. Major US law firms have issued advice to clients and companies to reduce the chances of AI chats winding up in court.