Hitbot is a kind of a link spidering program which can go for 8-10 level depth!(Using proxies,accepting cookies vs vs.)... Useually coded via c programming language and running on your server fully behaving like a human click...
A very well coded hitbot can really not be determined and all(!) toplists,counters,link traders etc. takes your fake traffic and sends you back real trafffic!
A very known method to find if someone is hitbotting you is to put a <a href="hllp://your.log.file.url"> tag which is an invisible link for real visitors but not for most(!) hitbots...So the hitbot clicks that link and u will see that somebody is somehow clicking an invisible link in your log file
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I suggest all adult webmasters here to put at least 3 invisible links like that in their page!
Hitbots are being sold for thousand dollars
Hope this info will be enough cluelessdomainer