Universal Advertising Systems gives its address as a post office box in Aruba.
The Montana Office of Consumer Protection confirmed this week that it is investigating the organisation following complaints that Universal Advertising Systems has sent out unsolicited e-mails, failed to deliver goods, and refused to honour refunds.
The FBI is conducting a separate investigation.
UK small businesses have complained to the police that their Demon e-mail accounts have been hijacked to send out spam e-mails, flooding their systems with thousands of undelivered messages.
The e-mails appear to be sent from Korea. Callers to the phone number given in the e-mail reach a company called Windsor Judicial Processing, in Billings Montana, which is just a forwarding address.