DEEP#DOOR is a Python-based backdoor campaign targeting Windows systems by disabling security controls and stealing credentials stored in browsers and cloud services. Attackers use tunneled command-and-control channels to avoid detection by standard network monitoring tools. Note: DEEP#DOOR reporting originates from a single third-tier source with no corroborating primary-tier vendor or government analysis; technical details and IOCs should be treated as preliminary. Organizations exposed to this threat risk unauthorized access to cloud infrastructure, privileged accounts, and sensitive business systems without visible indicators on the network perimeter.