Disclosed is an information protection system of an on-line service provider connected with customers' telephones through a telephone network for protecting important personal information of the customers from being leaked by tapping the customers' telephone lines, which includes an IVR system for collecting the customers' information-input patterns based on the customers' information-input signals received from the telephones and transmitting colored signals similar to the customers' information-input signals through the telephone network to the customers' telephone lines, and a control device for generating respective the colored signals similar to the customers' information-input signals based on the customers' information-input patterns, the colored signals being delivered to the IVR system. The IVR system transmits the colored signal to the customer's telephone line to scramble the customer's personal information being inputted. An echo canceller is provided to recover the customers' personal information from the scrambled information. An information-input pattern analyzer is provided to analyze the information-input pattern data to determine the customers' respective mean information-input patterns.