Machine learning: A new cyber security weapon, for good and ill

It's generating a great deal of interest, getting substantial backing from venture capitalists and even being billed as a must-have addition to the cyber-security arsenal. The idea of machine learning has been around for many years but today's realisations differ radically from earlier technologies. In simple terms machine learning software has no programmed-in knowledge about the domain to which it is to be applied but gains that knowledge by being taught. For example if you want to develop a machine-learning based optical character recognition system you feed it with many images of letters of the alphabet and you tell it "this is an'A' this is a'B'" and so on. Given sufficient data correctly identified, it will get very good at optical character recognition.