As the clock ticked down to midnight on December 31, 1999, the world held its breath. Experts warned that airplanes would fall from the sky, nuclear power plants would melt down, and the global banking system would collapse—all because early computer programmers had used two digits instead of four to represent the year. This was the Y2K bug, the first global panic of the digital age. "The Bug That Cost Billions" revisits the hysteria and the massive engineering effort that took place behind the scenes. It tells the story of the army of retired COBOL programmers who were called back into service to patch billions of lines of code in legacy systems. It explores the survivalist movement that stocked up on canned food and ammo, convinced that civilization would end when the calendar flipped. Crucially, the book addresses the modern misconception that Y2K was a hoax because "nothing happened." It argues that nothing happened precisely because $300 billion was spent fixing it. It is a fascinating case study in prevention paradox: when you successfully prevent a disaster, everyone assumes the danger was never real.