A test system for testing the robustness of at least one target system against 4he distributed denial-of-service, DDoS, attacks, the system by comprising: - at least one cloud management system for managing at least two cloud service providers for creating a distributed virtual machine structure suitable for DDoS simulations; - at least two command control centers for operational control of at least two virtual machines of said distributed virtual machine structure operating in each data center of said at least two cloud service providers in order to perform at least one test attack against the at least one target system to be tested in each one of said data center; - at least one monitoring system that monitors live the health condition of the at least one target system to be tested during the test; - at least one attack surface analyzing system, which is connected with said at least two cloud service providers and the monitoring system and which determines test parameters by analyzing the at least one target system to be tested before the test; - at least one attack management system ensuring that the at least one target system is tested based on predefined attack types, by means of the at least two virtual machines operating on at least one cloud service provider of said at least two cloud service providers in accordance with the test parameters determined, wherein if the at least one target system blocks all the requests from the at least one cloud service provider of said at least two cloud service providers during the test, the test is continued using the at least two virtual machines operating on another cloud service provider of said at least two cloud service providers; and - at least one reporting unit which analyses the health condition of the at least one target system monitored by the monitoring system after the test attack and determines the robustness of the at least one target system against the distributed denial-of-service attacks. - at least one cloud management system for managing at least two cloud service providers for creating a distributed virtual machine structure suitable for DDoS simulations; - at least two command control centers for operational control of at least two virtual machines of said distributed virtual machine structure operating in each data center of said at least two cloud service providers in order to perform at least one test attack against the at least one target system to be tested in each one of said data center; - at least one monitoring system that monitors live the health condition of the at least one target system to be tested during the test; - at least one attack surface analyzing system, which is connected with said at least two cloud service providers and the monitoring system and which determines test parameters by analyzing the at least one target system to be tested before the test; - at least one attack management system ensuring that the at least one target system is tested based on predefined attack types, by means of the at least two virtual machines operating on at least one cloud service provider of said at least two cloud service providers in accordance with the test parameters determined, wherein if the at least one target system blocks all the requests from the at least one cloud service provider of said at least two cloud service providers during the test, the test is continued using the at least two virtual machines operating on another cloud service provider of said at least two cloud service providers; and - at least one reporting unit which analyses the health condition of the at least one target system monitored by the monitoring system after the test attack and determines the robustness of the at least one target system against the distributed denial-of-service attacks.