Security protection for a host computer in a computer network using cross-domain security-relevant information

A computer-implemented method and system for protecting a host computer in a computer network from security threats uses local security-relevant data for the host computer, as well as global security-relevant data for other components in the computer network downloaded from a security information plane system to the host computer, to determine a security threat to the host computer. When a security threat is determined to be a legitimate threat, a security alert is issued, and then an action is initiated in response to the security alert.