With the large volumes of offshore wind to be installed in the coming decades and the increasing demand for interconnection between countries, it is to be expected that cross-border offshore High Voltage Direct Current (HVDC) electricity infrastructure is developed. Current HVDC infrastructure is based on point-to-point connections delivered by one vendor. However, for offshore grid development, multi-vendor, multi-terminal HVDC grids are used. HVDC infrastructure is usually protected by control and protection systems located at converter stations. With single-vendor, point-to-point infrastructure, these systems could be black boxed by their vendors. However, in a multi-vendor situation, this is not always possible. This has consequences for the IP strategy that vendors use but also for cybersecurity aspects of the system. After a short background on offshore HVDC systems, this chapter treats the shift from single- to multi-vendor systems and the cybersecurity threats and protection thereof. The chapter also sheds light on the legal framework on this issue, formed by the recent adoption of a Network Code on this matter and the NIS2 Directive.