[DarronWyke]

Symbiont. The word you're looking for is symbiont, not parasite. A symbiont lives in harmony with the host, exchanging something in exchange for the resource it consumes (in this case protection). A parasite just takes, and gives nothing back to the host.

(Of course, let's ignore the obvious joke about some AV solutions like Symantec.)

[cwyers]

Given your definitions, I'm pretty sure commercial AV is just parasites.

[TeMPOraL]

Yeah, the distinction between a symbiont and a parasite is mostly of degree, not kind, and AV software these days is increasingly being found on the blurry line between the two.