Microsoft windows represents the vast majority of home PC and a big number of servers as well. Because of its widespread and the complexity of its code (and probably the complexity of the coding processes...) a lot of vulnerabilities are discovered and exploited on this O.S. Windows is the main target of virus and malwares. Bankers, ransomers,ID stealers, D.O.S and spam bots, are the kind of malwares used by criminal organization to make millions of dollars. And nearly all this malwares target the Windows system. This section is focusing on threats targeting the Windows system and the security countermeasures.