One hindrance to the widespread adoption of mobile agent technology is the lack of security. Security will be the issue that has to be addressed carefully if a mobile agent is to be used in the field of electronic commerce. SAFER?or Secure Agent Fabrication, Evolution, and Roaming?is a mobile agent framework that is specially designed for the purpose of electronic commerce (Zhu, Guan, Yang, & Ko, 2000; Guan & Hua, 2003; Guan, Zhu, & Maung, 2004). Security has been a prime concern from the first day of our research (Guan & Yang, 1999, 2002; Yang & Guan, 2000). By building strong and efficient security mechanisms, SAFER aims to provide a trustworthy framework for mobile agents, increasing trust factors to end users by providing the ability to trust, predictable performance, and a communication channel (Patrick, 2002). Agent integrity is one such area crucial to the success of agent technology (Wang, Guan, & Chan, 2002). Despite the various attempts in the literature, there is no satisfactory solution to the problem of data integrity so far. Some of the common weaknesses of the current schemes are vulnerabilities to revisit attack when an agent visits two or more collaborating malicious hosts during one roaming session and illegal modifi- cation (deletion/insertion) of agent data. Agent Monitoring Protocol (AMP) (Chionh, Guan, & Yang, 2001), an earlier proposal under SAFER to address agent data integrity, does address some of the weaknesses in the current literature. Unfortunately, the extensive use of PKI technology introduces too much overhead to the protocol. Also, AMP requires the agent to deposit its data collected to the agent owner/butler before it roams to another host. While this is a viable and secure approach, the proposed approach?Secure Agent Data Integrity Shield (SADIS)?will provide an alternative by allowing the agent to carry the data by itself without depositing it (or the data hash) onto the butler. Besides addressing the common vulnerabilities of current literature (revisit attack and data modification attack), SADIS also strives to achieve maximum efficiency without compromising security. It minimizes the use of PKI technology and relies on symmetric key encryption as much as possible. Moreover, the data encryption key and the communication session key are both derivable from a key seed that is unique to the agent’s roaming session in the current host. As a result, the butler can derive the communication session key and data encryption key directly. Another feature in SADIS is strong security. Most of the existing research focuses on detecting integrity compromise (Esparza, Muñoz, Soriano, & Forné, 2006) or on bypassing integrity attacks by requiring the existence of a cooperating agent that is carried out within a trusted platform (Ouardani, Pierre, & Boucheneb, 2006), but which neglected the need to identify the malicious host. With SADIS, the agent butler will not only be able to detect any compromise to data integrity, but to identify the malicious host effectively.