A Cyber-Physical System (CPS) is a cross-domain system integrating sub-systems from multiple domains connected through communication networks. Today, CPSs can be found in various critical infrastructure areas such as aerospace, automotive, energy, healthcare, manufacturing transportation, entertainment, and consumer appliances. Although modeling and simulating systems and multi-physics behavior of CPS using first principle-based equations have been a continuing research endeavor, ubiquitous use of Internet of Things (IoT) is expected to increase the amount and diversity of data that can be acquired from the physical system. In such scenarios, it is imperative to fuse these data with the first principle-based equations to model and maintain those during runtime. In this talk, we will present, how these runtime models can be used for various purposes in CPSs - quality control, intrusion detection system, and creating new security related vulnerabilities.