To harness the safe operation of web-based systems in web Environments, the authors propose an SSPA (Server based SHA-1 Page digest Algorithm) to verify the integrity of web contents before the server issues an HTTP response to a user request. In addition to standard security measures, their Java implementation of the SSPA, which is called the Dynamic Security Surveillance Agent (DSSA), provides further security in terms of content integrity to web-based systems. Its function is to prevent the display of web contents that have been altered through the malicious acts of attackers and intruders on client machines.