I'm definitely guessing it's hijacking spyware.
I can imagine the algorithms in such:
"Redirect during randomized time-intervals" - On/Off...
I think the Adult industry needs to create & distribute an own equivalent
to AdAware / SpyBot Search-And-Destroy.
The regular software used either don't catch the crap doing this or a great
deal of all surfers just have not even heard about these things.
If one would put on a tin-foil hat... one could start suspecting all kinds of things.
The only thing I'm thinking now though... is that hijacking IS happening.
The question is: is it really THIS big?
