The campaign’s success is a dramatic illustration of the danger software flaws pose even years after they’re discovered and made public. Zero-day attacks —hacks exploiting previously unknown weaknesses—pack a punch and demand attention. But known flaws remain potent because networks and devices can be difficult to update and secure with limited resources, personnel, and money. Rob Joyce, a senior National Security Agency official, explained that the advisory was meant to give step-by-step instructions on finding and exploring the hackers. “To kick [the Chinese hackers] out, we must understand the tradecraft and detect them beyond just initial access,” he tweeted ....