Basically the setting is a futuristic earth, and they have brain implants that can give people access to an advanced form of something like google glasses. They can detect whether or not people have good or bad intentions toward you, highlighting in green or red. They are used by the military for tactical advantage, and normal people use them for browsing, driving, and such. They also have a built in kill switch that only the inventor knows about, and he is gathering information to use to kill people who meet a certain profile. I believe this profile was people who were either greedy or some other quality the inventor deemed bad.
Somehow its found out, and some people (I think like FBI agents) try to stop him, and end up getting help from a hacker who helps them change the filter to something that exactly fits the inventor and it ends up killing the inventor and only a few others.
I read it within the past 5 years, but it wasn't a new book at the time. I think it had been out for a few years when I read it, so I would guess the book is probably no more than about 7 years old.
I don't really remember the cover.
More info/clarifications: By futuristic Earth, it is basically just a more technologically advanced Earth, so maybe like 50 years into the future or something. The implants can read brain waves and use an algorithm to predict behavior and personality traits. Military use it to detect whether people are hostile or not, and ordinary people use it to browse the web, gps, etc. The inventor either was a hacker, or worked with a hacker to develop the algorithm, and the people trying to stop the kill switch from going off reach out to that hackers rival.
The hacker that helps them stop the kill switch says the only way to get a meeting with the person responsible is for him to deface the FBI website with porn or something like that. That act will outdo the other hackers greatest achievement and force the other hacker to give a trophy of some sort.
I remembered another bit from the story. Maybe it will help identify the book. These implants/chips had to be surgically implanted, in the head, and they seemed to integrate with the optic nerve, so that images were able to be projected onto their vision, and they could navigate on this overlayed visual by looking. One person was killed when the inventor took advantage of this, and caused the device to block out the input from the eyes and replace it with an incorrect landscape while the person was driving. This caused the driver to accidentally drive off the road, because he saw a straight road where it actually made a turn.