From Wikimon
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Tempest (テンペスト Tenpesuto) is a crack program that the Seven Great Demon Lords had secretly released into the Digital World. One of the main effects in the DigiCore of an infected Digimon consists in overwriting their digital data naturally expressed in binary and being converted into ternary, causing the Digimon to go wild and lose control, infecting other Digimon in the process.

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As a result of the crack software, this affected not only the Four Holy Beasts, who protected the Digital World, but a number of Digimon throughout the plain causing widespread chaos. In the attempt to resolve the Tempest crisis, the Digimon Twin was formulated; but this however would go on to create future problems and conflicts, i.e. the L&R Wars and the Xros Wars.