Systems for preventing pestware activity are described. One embodiment a heuristic engine configured to identify repeat pestware activity and configured to block the repeat pestware activity; an operating system pestware shield in communication with the heuristic engine, the operating system pestware shield configured to detect pestware activity and report the pestware activity to the heuristic engine; and a browser pestware shield in communication with the heuristic engine, the browser pestware shield configured to detect pestware activity and report the pestware activity to the heuristic engine.