“Carry out all my demands or the entire country’s electricity will be cut off.” Is this another line from a suspense film, or is it a palpable threat made possible with a computer keyboard? “Today, there is a growing trend amongst hackers around the world to threaten national infrastructures for ransom,” says Dr. Yaniv Levyatan, an expert in information war at the University of Haifa.

If someone still thinks that this is science fiction, Dr. Levyatan notes how just recently, in Nov...