In a world which is every day more interconnected and permeated with social relationships (both physical and virtual) modelling such interactions has become an interesting point mostly to achieve a better comprehension of phenomena such as the raise of communities. From a mathematical perspective the general theory of unsigned networks - where nodes are linked one to each others by positive arcs representing the intensity of the links - seems not optimal to describe such situations and signed networks are commonly used in order to take into account also negative interactions (enmity). Referring to Cartwright and Harary's generalization of Heider's theory, the two theories of structural balance and weak balance have been developed in order to investigate the cause of conflicts in networks of individuals whose mutual relationships are characterizable in terms of friendship and hostility.