  In this paper, we propose a game-theoretical framework to investigate
advanced persistent threat problems with two types of insider threats:
malicious and inadvertent. Within this framework, a unified three-player game
is established and Nash equilibria are obtained in response to different
insiders. By analyzing Nash equilibria, we provide quantitative solutions to
the advanced persistent threat problems with insider threats. Furthermore,
optimal defense strategy and defender's cost comparisons between two insider
threats have been performed. The findings suggest that the defender should
employ more active defense strategies against inadvertent insider threats than
against malicious insider threats, despite the fact that malicious insider
threats cost the defender more. Our theoretical analysis is validated by
numerical results, including an additional examination of the conditions of the
risky strategies adopted by different insiders. This may help the defender in
determining monitoring intensities and defensive strategies.
