Customer views thru a customer portal link

Customer views thru a customer portal link

When you establish a Customer Portal, and share it with the group of customers, can each customer see the others transactions or are they only viewing their individual transactions.

My objective is that the customer logged in only views their own transactions and no one else. 

For example:
Portal link is shared with Customers A, B and C. When Customer B signs in do they see transactions related to Customer A and or C?

 Is this correct?