The Covid-19 pandemic has multiplied false content in the public sphere, in a phenomenon that the World Health Organization has described as a global 'infodemic'. The dynamics of public disinformation already existed long before the arrival of the internet and the pandemic, but the conjunction of these two elements has led to an exponential growth of falsehoods. In this context, the term "fake news" has become widespread to label all forms of modern misinformation. However, the typology of hoaxes and disinformation procedures are much more complex than it seems. Based on the findings of the RRSSalud research project, where the team of Prof. Salaverría at the University of Navarra is working together with researchers of Barcelona Supercomputing Center, this presentation will analyze the origin, multiple forms and mechanisms of disinformation in the sphere of social networks.