Properly done with a large enough website network and a large enough bot network and enough AdSense accounts, such activity could be hard for Google to detect if done properly.
Whether or not adware/spyware detectors detect such infestations will depend upon how up to date such detectors are and how sneaky these zombie programs are. Still there are millions of improperly protected computers attached to the Internet, so for the operators of these zombie networks such security programs don't pose a big threat.
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