N.J. water systems are exposed to hackers. A near-disaster in Florida shows the threat. Updated 3:00 PM; Earlier this year, the plot of a spy thriller unfolded at a Florida water treatment plant. Without warning, hackers breached the computer system operating the plant on Feb. 5, boosting treatment chemicals to dangerous levels. A water operator at the plant could only watch as a remotely controlled mouse drifted across his computer screen, skyrocketing levels of lye — a caustic chemical used to control water acidity and remove harmful metals from drinking water — from the usual 100 parts per million to a highly toxic 11,100 parts per million.