## 1 Introduction  
Incidents such as an escalation of Houthi attacks on shipping through the Red Sea [1], blockage of the Suez Canal by [PERSON] in 2021 [2] and the paralysis malware attack on shipping giant Maersk in 2018 [3], underscore both the critical importance of the maritime transportation system (MTS) to global supply chains and its acute vulnerability to disruptive kinetic, cyber, or cyber-physical attack. This article will discuss hybrid threats to the MTS in response to three broad research questions: first, what are the greatest hybrid threats to maritime security, taking account of the unique nature of Information Technology (IT) and Operational Technology (OT) systems in ships? Second, who are the most likely non-state actors to exploit such weaknesses and what are the likely attack vectors? Third, what governance regimes exist at the intersection of maritime security and cybersecurity to protect or mitigate against hybrid attacks on shipping? As a lens through which to view and discuss hybrid maritime security and its governance the article focusses on shipping through one of the world's most congested shipping chokepoints, the Straits of Malacca and Singapore (the \"SOMS\"). Policy recommendations arising from research are relevant and applicable to hybrid maritime security in international shipping in general, and to other strategic global chokepoints in particular, such as the Bab Al Mandeb strait, Suez Canal, Panama Canal, and others [4]. Following a literature review setting out the background and current landscape in the field of maritime hybrid security in general, the results of the mixed-methodology research combining primary sources (survey, interview and roundtable discussions) and secondary sources (academic literature, grey literature and media reporting) groups its findings into five broad categories forming the overall structure of the article as follows. Results informed by survey: (1) broad industry and academic views on the current state of Information and Communication Technology (ICT) and emerging technology, security, and governance in the maritime sector. Results from the survey then guided more in-depth exploration of issues informed by interview and roundtable discussion results: (2) threat analysis of global shipping; (3) threat analysis focussed on the SOMS littoral states of Indonesia, Singapore, and Malaysia (and activities in adjacent countries that impact security in the SOMS such as terrorist and pirate activity originating from the Southern Philippines); (4) global governance (that is results that apply to the governance of hybrid security in international shipping in general); and (5) regional governance (results that are specific to the governance of hybrid maritime security in the region of Southeast Asia and the SOMS littoral states in particular). Survey results indicate strong support for several key findings: (1) Information and Communication Technology (ICT), networked devices, and emerging technology onboard ships creates new challenges for maritime security; (2) current levels of cybersecurity in ships are insufficient; (3) criminal cyber attacks on the maritime sector have occurred in the past and will continue to be exploited by criminal groups; (4) cybersecurity in the maritime sector lags behind other sectors; and (5) current regulations are insufficient to address challenges posed by new technology. Interview and roundtable results support several key findings relevant to categories 2, 3, 4, and 5 above: multiple factors contribute to vulnerabilities of ships to cyber attack--a convergence of IT and OT systems, greater connectivity through Low Earth Orbit (LEO) satellites, outdated legacy software and hardware, and a paucity of information sharing about cyber attacks in the maritime sector.