A mysterious yellow box popped up on websites in the U.S. and Australia Tuesday evening for around 45 minutes, costing Google millions and providing a windfall for publishers. It turns out that an employee accidentally purchased "300x250 ad units" for Australian retailer The Iconic during a training session, according to AdAge. The ad campaign reportedly spent over $1.6 million in less than an hour, costing Google a hefty sum. AdExchanger writes that the "scale of the mistake is unprecedented and the worst in memory."