White House officials concerned about AI chatbots' potential for societal harm and the Silicon Valley powerhouses rushing them to market are heavily invested in a three-day competition ending Sunday at the DefCon hacker convention in Las Vegas. Some 3,500 competitors have tapped on laptops seeking to expose vulnerabilities in eight leading large-language models representative of technology’s next big thing. But don’t expect quick results. Identifying and fixing flaws will take time and many millions of dollars. Current AI models are simply too unwiedly, brittle and malleable, academic...