This paper investigates the connection between network reliability and security by modeling attacker-defender interactions as a game. We model the defender's network as an undirected graph with insecure and unreliable edges. The edges could either fail due to a random malfunction (fault), or due to a strategic attacker who aims to maximize the defender's loss (attack). In many environments, the defender faces prohibitive costs of isolating the type of failures, i.e., fault versus attack. In addition, delays in arrival of diagnostic information to the defender may prevent him to detect the type of failure. To account for such information deficiencies, we let the defender know only the relative frequencies of failures with different types. From our analysis, equilibrium depends on these relative frequencies, and on the exogenously given probability distribution of reliability failures on the edges. Thus, in presence of the aforementioned information deficiencies, reliability and security are interdependent, and we argue that defenders (managers) should co-design their defenses against faults and attacks.