This paper analyzes the intrinsic vulnerability problems of the authentication system for Internet commerce based on the ID and password strings gathered from the computer keyboard. Through the found vulnerability, it is easy to sniff user passwords as well as any other keyboard inputs even when each of the existing keyboard protection softwares is running. We propose several countermeasures against the possible attacks to the vulnerability at both points of the hardware and the software concerns. The more secure environment for Internet commerce is highly required by implementing the proposed countermeasures.