Vulnerability of telephone systems

Telephone companies are investing heavily in advanced computer systems to manage their networks. In general this lowers costs and makes calls connect more quickly, and permits a greater variety of voice and data services. However it also increases the degree of central control such that any failure, even at a local level, can have unforeseen widespread effects.

In 1990 in the USA a small computer error at an exchange in New Jersey led to a major failure of a continent-wide telephone network over a period of 9 hours, during which 50% of the long-distance calls could not be made.