The Savage Aether. The Savage Aether, #1

Welcome to your Technofeudalist future... As the sun rises it burns over the seawalls that holds the ocean from the remains of the city. Society runs on the Uplink, a global pseudotelepathic social network that interfaces directly with the brain, connecting people with a constant barrage of information. Those whose brains don't fit the mould of the Uplink's servers are left searching for scraps in the remains of the city, often fit with body modifications and doing demeaning work.
They call them Augs. Colin and his sister Cass are facing two sides of the same problem. It's suspected that a group of Augs are trying to hack the Uplink's systems, to gain access to the network that makes a normal life possible. Col is working in the datacentre, where parts have started going missing. His sister, a freelance journalist hunting rumours, has found a secretive Aug group that she suspects is responsible for the thefts.
But when the latest upgrade to the Uplink goes live, Colin passes out in sudden pain. When he comes to, he can't get access to the network, or to Cass. Alone but for another lost soul named Ariana, he begins to hunt for his sister. Along the way he learns more about the Augs, and discovers the savagery at the core of the system.