Direct calque of English "botnet". 僵尸 means "zombie" (in Chinese folklore, a stiff hopping corpse), here used in the IT sense - a machine that does the master's bidding without its owner's knowledge.
culture
The Chinese 僵尸 is its own folkloric creature distinct from Western zombies - a Qing-dynasty stiff-jointed hopping corpse, popularized worldwide by the Mr. Vampire (僵尸先生) HK film series. The IT sense is purely a 1990s loan.
