A central computer system transforms identification information of a consumer into an identity code that hides the identification information and stores it with contact information of a consumer's computer system. When a computer system on the network of the central computer system conducts a transaction with a subject who uses the identity code of the consumer, the central computer system contacts the consumer's computer system so that the consumer can stop the transaction if it is not authorized. Because only the identity code is used to protect the consumer, the original identification information of the consumer is fully protected.