The Origin of ANCs:

Takashi Okamura was brought into the hospital in Tokyo after collapsing at work. He was diagnosed with a brain tumor. When they attempted to repair it, however, the monitors started malfunctioning. They delayed the test because of this complication and when they thought they had fixed the problem they tried again. This time, however, the monitors started malfunctioning before they hooked him up. Over the next week they set up for a low tech surgery and, when they were done, removed a golf-ball sized tumor from his brain. Afterwords he was no longer able to disrupt the equipment, but if he concentrated enough he could disrupt his Ipod.
When they heard of the case, the Japanese military bought the tumor from a nurse who had the sense to save it. They gave it to an medical device company that scanned it and reproduced it as an electric circuit. After training, some of the scientists were able to move small objects or disrupt small electronic devices. There was even a report of one who could read the surface thoughts of his coworkers. Over the years they made improvements to the design and eventually miniaturized it and turned it into a medical implant.
A few years later the technology is located in the United States. It was leaked as the result of corporate espionage, but as a result became one of the most important pieces of technology developed in the last century.

ANC Overload:
ANCs have been known to cause brain damage, aneurisms, seizures, and, in rare cases, brain tumors. There are two common reasons for this. The most common reason is that a person has tried to force the ANC to operate beyond its maximum safe level. The second reason is that the person's brain doesn't have the skill to safely operate the ANC.
All ANCs have a minimum level of skill that they can be safely operated at. If you don't have that minimum level of skill, your brain experiences stress akin to trying to solve a calculus problem when you only know algebra. They also have a maximum level that they can be used at, as they generate exponentially more heat the more heavily they are used. This heat disrupts the effect, which makes it weaker. The maximum safe level is the point at which the effect starts to break down.