They were using iframes to drop cookies on visitors computers without them actually intending to go to eBay - or even being aware that they had "visited" eBay a

They were using iframes to drop cookies on visitors computers without them actually intending to go to eBay - or even being aware that they had "visited" eBay at all. This is against the ToS, but isn't necessarily a crime. The crime was their attempts to obfuscate and hide the activity so that eBay could not legitimately tell if they were doing so against the ToS. Fraud includes intentionally deceiving someone in the context of an agreement, statement or contract (iirc). They got caught because they made a long-running habit of hiding their illicit activity to a degree which made them guilty.