From The New York Times
Though it was the kind of chaos that malevolent computer intruders always seem to be creating in the movies, the problem was traced to a malfunctioning network card on a desktop computer. The flawed card slowed the network and set off a domino effect as failures rippled through the customs network at the airport, officials said.
[. . . ] experts say that some of the most serious, even potentially devastating, problems with networks arise from sources with no malevolent component.
The complete New York Times story