Virus Core

Virus Cores are the creation of King Drasil, as the beginning of his plan to reset the Digital World. When a Digimon comes in contact with a Virus Core, their own DigiCore becomes corrupted and they go insane. The first victims of the Virus Cores were Omnimon, Beelzemon, and BlackWarGreymon.

When an infected Digimon is killed, the Virus Core jumps into closest Digimon to it. The only way to permanately get rid of a Virus Core is for Reign to digitize the infected Digimon's Fractal Code with his Digivice, turning them back into a Digi-Egg.

When King Drasil was destroyed, the Virus Cores vanished for good.