Modern power systems are increasingly complex and uncertain with changes in load and generation at all voltage levels. This condition prompts the need for greater monitoring and analysis of power system dynamic security. This is increasingly true as significant new transmission assets such as HVDC lines are introduced into networks. This paper presents a thorough investigation of the impact of HVDC integration on all aspects of dynamic security including small-disturbance stability, transient stability, frequency stability, and voltage stability. Both parallel and infeed VSC-HVDC lines are incorporated into a two-area network in order to establish the impact of HVDC on system performance across all dynamic security aspects. The results obtained show that significant improvements in voltage stability margins can be obtained, however some other aspects of dynamic security are impacted negatively.