Method for communication between secured computer systems (WS, WS1, WS2, PS), comprising the steps: - providing a prepared task file in a task computer system (TS1, TS2), - transmitting the prepared task file from the task computer system (TS1, TS2) to a source computer system (WS, WS1, WS2), - supplementing the prepared task file with specified information in the source computer system (WS, WS1, WS2), - transmitting the supplemented task file from the source computer system (WS, WS1, WS2) to the task computer system (TS1, TS2), - transmitting the supplemented task file from the task computer system (TS1, TS2) to a target computer system, - verifying the validity of the supplemented task file by the target computer system, - executing at least one task in the target computer system on the basis of the supplemented task file in the event that the verification of the validity of the supplemented task file was successful, wherein both the source computer system (WS, WS1, WS2) and the target computer system at least temporarily keep specified network ports closed such that addressability of the source computer system (WS, WS1, WS2) or of the target computer system via a network for storing or fetching the task file is prevented, but the task computer system (TS1, TS2) is accessible with at least one listening open network port via network in such a way that the source computer system (WS, WS1, WS2) or the target computer system can access the task computer system (TS1, TS2) in order to store the task file in the task computer system (TS1, TS2) or fetch it from the task computer system (TS1, TS2), and wherein the transmission of the supplemented task file from the task computer system (TS1, TS2) to the target computer system includes the following steps: - sending a specified sequence of package data from the task computer system (TS1, TS2) or source computer system (WS, WS1, WS2) to the target computer system, wherein the specified network ports of the target computer system are closed, and wherein the sequence addresses one or multiple network ports of the target computer system in a specified order, - verifying the sent sequence for conformance with a predefined sequence in the target computer system, as well as - initiating the transmission of the supplemented task file by the target computer system in the case that the verification of the sent sequence has been positive, wherein the target computer system establishes a connection to the task computer system (TS1, TS2) and fetches the supplemented task file from the task computer system (TS1, TS2). - providing a prepared task file in a task computer system (TS1, TS2), - transmitting the prepared task file from the task computer system (TS1, TS2) to a source computer system (WS, WS1, WS2), - supplementing the prepared task file with specified information in the source computer system (WS, WS1, WS2), - transmitting the supplemented task file from the source computer system (WS, WS1, WS2) to the task computer system (TS1, TS2), - transmitting the supplemented task file from the task computer system (TS1, TS2) to a target computer system, - verifying the validity of the supplemented task file by the target computer system, - executing at least one task in the target computer system on the basis of the supplemented task file in the event that the verification of the validity of the supplemented task file was successful, - sending a specified sequence of package data from the task computer system (TS1, TS2) or source computer system (WS, WS1, WS2) to the target computer system, wherein the specified network ports of the target computer system are closed, and wherein the sequence addresses one or multiple network ports of the target computer system in a specified order, - verifying the sent sequence for conformance with a predefined sequence in the target computer system, as well as - initiating the transmission of the supplemented task file by the target computer system in the case that the verification of the sent sequence has been positive,