The computer-related risk of the year: weak links and correlated events

There has been much innovative work in designing computer and communication systems that can dependably attain certain stringent requirements such as multilevel security, very high availability, or functional correctness. However, significant risks may remain if such a system fails to operate as expected. A variety of causes must be considered. A confluence of unrelated or seemingly unrelated events such as malicious misuse and faults that exceed the system fault tolerance may cause the system to behave in an unanticipated way. The 1991 Risk of the Year designation recognizes such eventualities. Three types of cases are considered: notably weak links, independent multiple events and correlated multiple events. Not surprisingly, the three cases are often discovered to be interrelated, even when seemingly disjoint