The security of supply chain management (SCM) concerns the information security of various interactions among SCM’s drivers. Each driver requires a different i-security level relevant to the services it contributes to the overall supply chain. Hence there is a demand to have a measuring tool of i-security level for each driver and its impact on the other drivers’ i-security. This research proposes an i-security model in which each of the basic goals of i-security, i.e., confidentiality, integrity, availability and accountability (CIAA) are assigned a different weight appropriate to the driver’s mission. A semi-Markov chain model is used to describe a probabilistic nature of different i-security levels for each driver in SCM. This model is used to present several scenarios with different levels of attackers to present different i-security responses. The analysis should help to compare the levels of i-security, and to point out the vulnerabilities in SCM information system, and should be especially useful to professionals in information security fields, or anyone who may be consider developing online electronic commerce.