Machine Learning (ML) is one of the greatest creations in the last decades. It has been defined for the first time by Arthur Samuel in 1959 as "the field of study that gives computers the ability to learn without being explicitly programmed". ML has completely changed the way of programming: with just a single program, the machine is able to learn by itself how to perform many different tasks. Even though Machine Learning is not a recent creation, it only developed in the last years. The main reason is the progress of the technology and the growth of internet. Basically, there are much larger data sets to exploit than ever before.