Some of their partners are so lame, that their clickbots don't even pull any image files with their bot. I was just looking through my logs and saw quite a few new search "partners" that don't even have enough money to have someone write a decent bot that at least appears to be a human visitor. All these bots are pulling is the index file and that's it.
When ( rhetorical question) will yahoo put an end to these nefarious partners and allow us to only get yahoo traffic? If they wanted to see more advertising dollars, they would put an end to this nonsense.
Heck I'd rather get crappy human arbitrage traffic that got paid to click over a bot, as 1 in a million crap traffic will convert.