Method for unblocking external computer systems for communication with secured processing computer systems (target server) in a computer network infrastructure, comprising the steps: - transmitting an authentication packet from an external computer system, which is configured outside the computer network infrastructure, to a broker computer system (task server) within the computer network infrastructure, wherein the authentication packet contains signed information for authentication of the external computer system, - automatedly transmitting the authentication packet from the broker computer system (task server) to at least one processing computer system (target server) within the computer network infrastructure, wherein the processing computer system (target server) communicates, via a network (N, N3), with the broker computer system (task server), wherein the processing computer system (target server) keeps predetermined network ports at least temporarily closed, so that any access to the processing computer system (target server) via the network (N, N3) is prevented by means of these network ports, wherein, however, the processing computer system (target server) accesses the broker computer system (task server) via the network (N, N3) in order to fetch the authentication packet from the broker computer system (task server), - verifying the authentication packet in the processing computer system (target server), - unblocking at least one selective network port by the processing computer system (target server) for communication with the external computer system, if the verification of the authentication packet in the processing computer system (target server) was successful, - establishing a connection to the selectively unblocked network port of the processing computer system (target server) by the external computer system. - transmitting an authentication packet from an external computer system, which is configured outside the computer network infrastructure, to a broker computer system (task server) within the computer network infrastructure, wherein the authentication packet contains signed information for authentication of the external computer system, - automatedly transmitting the authentication packet from the broker computer system (task server) to at least one processing computer system (target server) within the computer network infrastructure, wherein the processing computer system (target server) communicates, via a network (N, N3), with the broker computer system (task server), wherein the processing computer system (target server) keeps predetermined network ports at least temporarily closed, so that any access to the processing computer system (target server) via the network (N, N3) is prevented by means of these network ports, wherein, however, the processing computer system (target server) accesses the broker computer system (task server) via the network (N, N3) in order to fetch the authentication packet from the broker computer system (task server), - verifying the authentication packet in the processing computer system (target server), - unblocking at least one selective network port by the processing computer system (target server) for communication with the external computer system, if the verification of the authentication packet in the processing computer system (target server) was successful, - establishing a connection to the selectively unblocked network port of the processing computer system (target server) by the external computer system.