Do you get any spam for "My Canadian Pharmacy," "Canadian Health&Care Mall," "International Legal Rx Medication," "Men+ Health," "US Drugs," or "VIP Pharmacy ('Viagra + Cialis')?" Those are all hosted on hijacked Unix servers. They also use other hijacked Unix servers to load their images and host their nameservers. The professionals that monitor those servers can't find the files because they load, execute, and delete commands as called for. The admins don't notice the "tirqd" trojan, whose name looks too much like a process that belongs there.
Oh, and the thousands of domain names for their websites are registered with stolen credit/debit cards, but Visa doesn't see that as any reason not to allow them to have a merchant account to sell their Viagra. (And Visa has been informed; Mastercard apparently thought that was good enough reason to drop the scammers, but you can still use Visa on their sites.)