The use of social media is not just a passing trend or fad; rather, it has become an essential aspect of every person's life. Consequently, with the increase of daily online interactions among users and the intensity of consumption, the way they engage with information- particularly during crises - has gained special importance. The emergence of the COVID-19 virus in December 2019 and the dissemination of news related to it, turned social media into a platform for the circulation of inaccurate and negative information. This study, this study aimed to design a model to explain the behavior of users in publishing fake news related to the Covid-19 virus, using a qualitative method and grounded theory. The data were collected through semi-structured interviews and analyzed using open, axial, and selective coding. The research findings revealed that three primary factors, including users' individual characteristics, the attributes of news content and country's media regime play a decisive role in the dissemination of fake news. Also, crises such as the COVID-19 pandemic, by increasing ambiguity and public sensitivity, accelerates the dissemination of such news. Based on the findings, Solutions were proposed at plural the micro (improving users' media literacy) and macro (increasing transparency in platform Policy-making) levels. The model presented in this study can be used as a practical tool for information management during crises.