Why would someone do such a thing? Profit, hatred, or shear sadistic pleasure: They may knowingly do it as well, if they were asked to do such a thing by someone higher up. The article “Why Good People Do Bad Things: The Case of Collective Violence” makes a case for computer use possibly leading to warfare against another country. War can be won by a number of ways. One of the most effective is to shutdown their infrastructure. If you hacked into an opposing country’s power systems, shut them down and then launched your own attack, you could achieve victory before the major population even realised they were under attack. In the far future, if we ever rely on computers and robots for our livelihood, doing such a thing could cause a major tragedy.
How can we protect ourselves, not from the computers and robots, but from our own species that wish to harm and control us!