Tai and Sora are currently in an arguement over how he gave her a hairpin for her birthday, and Tai is trying to apologize via e-mail. He and Kari argue a bit, and he finally chases her out of his room, and she goes to her birthday party. Izzy, in a fury, rushes to Tai's house because a Digimon is eating all of the Internet's data. He explains to Tai his connections with Willis while the two of them try to connect with Gennai. Gennai knows of the threat, and begins to upload Agumon and Tentomon onto the Internet.
The virus/Digimon has already Digivolved to Rookie, and Greymon and Kabuterimon corner him. Keramon then bypasses the Champion Level and Digivolves into his Ultimate Level, Infermon. Infermon easily trashes Greymon and Kabuterimon, to Tai's dismay. Infermon then travels to the computers in the United States, as he as already disconnected most phone companies in the Eastern Hemisphere. Izzy is unable to get anyone else to fight but Matt and T.K., who are at their grandmother's house. Sora is still too mad at Tai, Mimi's on vacation, Kari's busy at the party, and Joe is at summer school.
After linking up with Matt and T.K., MetalGarurumon and WarGreymon confront Infermon, whose first action is to mutate into his Mega Level, Diaboromon. WarGreymon and MetalGarurumon are crippled by the e-mails sent to Izzy to defeat Diaboromon. To make matters worse, Willis alerts Izzy that Diaboromon has crashed the Pentagon's computers. The U.S.'s computer system, under Diaboromon's control, launched two nuclear missiles: one heading towards Colorado, the other Japan. The world's armies try to knock them into the Pacific.
Meanwhile, Diaboromon has multiplied into over a million copies. WarGreymon and MetalGarurumon are too slow to fight because of the houndreds of instant messages and E-mails kids around the world are sending to Izzi. Then, somehow, WarGreymon and MetalGarurumon DNA Digivolve into Omnimon. Tai and Matt are now in the Internet with their new creation, and they use the e-mails to shut down Diaboromon's agility. He is destroyed by Omnimon, just before the bombs explode.