The advent of the Internet of Things (IoT) has ushered in the concept of smart cities – urban environments where everything from traffic lights to waste management is interconnected and digitally managed. While this transformation offers unparalleled efficiency and innovation, it opens the door to myriad cyber-attacks. Threats range from data breaches to infrastructure disruptions, with one subtle yet potent risk emerging: fake clients. These seemingly benign entities have the potential to carry out a multitude of cyber attacks, leveraging their deceptive appearance to infiltrate and compromise systems. This research presents a novel simulation model for a smart city based on the Internet of Things using the Netsim program. This city consists of several sectors, each of which consists of several clients that connect to produce the best performance, comfort and energy savings for this city. Fake clients are added to this simulation, who are they disguise themselves as benign clients while, in reality, they are exploiting this trust to carry out cyber attacks on these cities, then after preparing the simulation perfectly, the data flow of this system is captured and stored in a CSV file and classified into fake and normal, then this data set is subjected to several experiments using the Machine Learning using the MATLAB program. Each of them shows good results, based on the detection results shown by Model Machine Learning. The highest detection accuracy was in the third experiment using the k-nearest neighbors classifier and was 98.77\%. Concluding, the research unveils a robust prevention model.