Flynn had joined the U.S. military in 1981, at the height of the Cold War. He built his career in army intelligence, rising through the ranks in a force focused on the Soviet military machine. After 9/11, it all changed. He was made director of intelligence for the task force that deployed to Afghanistan to face a new kind of foe for which the military was ill-prepared. As the fighting against a distributed network of insurgents continued there and then expanded to Iraq, Flynn assumed the same role for the Joint Special Operations Command (JSOC)—the secretive organization for elite units like the Navy SEAL team that would ultimately kill Bin Laden (and, then proving the new power of OSINT, would have its own operations outed by a Pakistani café owner up late at night on Twitter). It was in this position, faced with the difficult task of tracking down the terror cells of al-Qaeda in Iraq, that Flynn realized his operatives had to look elsewhere, out in the open, for clues to where the enemy was hiding. And they had to do it faster than ever before.

As Flynn explained to The New Yorker’s Nicholas Schmidle, U.S. special-operations forces were commandos without equal, “the best spear fishermen in the world.” But in order to beat an adversary that recruited so rapidly and blended so easily with the civilian population, he told Schmidle, the commandos would have to become “net fishermen.” They would eschew individual nodes and focus instead on taking down the entire network. As Flynn’s methods evolved, JSOC got better and better, capturing or killing dozens of terrorists in a single operation, gathering up the intelligence, and then blasting off to hit another target before the night was done. Eventually, the shattered remnants of al-Qaeda would flee Iraq for Syria, where they would later reorganize themselves into the core of ISIS.

Flynn’s career took off. He was promoted to three-star general and, in 2012, appointed to lead the DIA, the agency charged with centralizing intelligence across the entire U.S. military. Although he had no experience commanding an organization so large (some 17,000 employees in all), Flynn was eager: He envisioned not just reform of the DIA, but a wider reorganization of how the entire intelligence system worked in the 21st century. Before the rise of social media, he explained, 90 percent of useful intelligence had come from secret sources. Now he saw it as the exact opposite, with 90 percent of the potential useful information coming from open sources that anyone, anywhere could tap.

The reason wasn’t just that the internet had grown; it had also started to change in another, more fundamental way. The literally billions of new users coming online were using computers far different than the ones first networked together in ARPANET, the Defense Department’s early version of the internet. They carried “sensors,” devices for gathering information about the world beyond the computer. Some sensors are self-evident, like the camera of a smartphone. Others lurk in the background, like the magnetometer and GPS that provide information about direction and location. These billions of internet-enabled devices, each carrying multiple sensors, are on pace to create a world of almost a trillion sensors. The current head of the U.S. Army, General Mark Milley, summed up the impact to us this way: “For the first time in human history, it is near impossible to be unobserved.”