An Nmap scan shows that ports 135, 139, and 3389 are open on a compromised device. What operating system is most likely running on that device?

The presence of open ports 135, 139, and 3389 strongly indicates that the device is running a Windows operating system. Port 135 is used by the DCOM (Distributed Component Object Model) service, which is associated with Windows network services. Port 139 is used for NetBIOS session services, allowing for file and printer sharing on Windows networks. Port 3389 is the default port for Remote Desktop Protocol (RDP), which is specifically designed for remote administration of Windows systems.

The combination of these ports is characteristic of Windows environments, and their presence on a device suggests it is likely compromised Windows system. Other operating systems such as Linux, macOS, and Unix do not commonly use these ports for their core services, making them less likely candidates in this scenario.