"So eBay installed a tiny “gif” file on its homepage. A gif is simply an image file. This one was so tiny no one could see it. It sat there invisibly."
A lot of things fall under wire fraud rules. A lot of very common and routine business practices qualify as wire fraud. The fact that that is the only charge is very telling.
So say eBay notices they are serving 1 million cookies a month to users, but only have 50,000 visitors relating to those people on their homepage. That's how they know this was cookie stuffing and not legitimate traffic.
Finding out how many IP's were legit vs bogus was then a simple matter of going through the http logs making sure all gets of the cookie had matching gets of the gif. Cookie gets without gif gets were fraud.
Or did they use another method to place the cookie I don't know about?
I don't know if that works anymore because my "affiliate" time is well long over but I guess this loophole has been fixed long since.
IIRC iframe was a little problematic with some websites as they had frame break out scripts [1] - so you had to be creative.
The golden wild west times ... I somehow miss them. Money was lying on the information super highway - you just had to pick it up ;)
[1] something like http://www.thesitewizard.com/archive/framebreak.shtml
It will be interesting to see how this goes in court since you cannot prove that any given single user was NOT a "real" user. But on the whole, the traffic smells wrong.
I don't understand why eBay didn't just ban the users when they suspected foul play. Trying to prove this criminally beyond a reasonable doubt would have been hard.