The merchant ID was assigned by the credit card processor and is the link to your account there. You may have received multiple merchant IDs, each relative to the credit cards that you will accept and process. This ID is used internally by the credit card processor and is not needed by the Merchant/400 API to execute a credit card transaction. The virtual terminal identification, received from the card processor, will be used by the partner processing agency to link your merchant name with the merchant ID.
The merchant name and password were assigned by your chosen partner processing agency. These are used to log on to their service to pass credit card transactions to the card processor. These are unique to your organization and should be kept in confidence, as they can be used not only to complete a credit card transaction, but also to make debit adjustments to your merchant account. Both entries are SSL encrypted (with the customer order and credit card information) when transmitted to the partner processing agency.