NetBIOS is a legacy API that was used for communication between systems on LAN. Each system had an unique NetBIOS name assigned to it. When a machine wanted to connect to other system, it would resolve the NetBIOS name of the target system to it’s corresponding IP address and then connect. NetBIOS had vulnerabilities and was an easy target for exploitation. Attackers could get the information like NetBIOS names, domain names, network shares etc.