The only instance somewhat like this that I am aware of is that two malware samples sort of 'recombined' accidentally. One was a worm that packaged itself up a

The only instance somewhat like this that I am aware of is that two malware samples sort of 'recombined' accidentally. One was a worm that packaged itself up and sent itself around, the other did some sort of injection or binary patching and happened to piggyback onto the worm.