## 4 Security of Computer Network Users  
The security of IoT users is a comprehensive and constant issue. Users of such networks can use banking or training platforms, Internet messengers (Messenger, Signal, WhatsApp), social networks (Facebook, Twitter), intelligent devices, or networks of vehicles. Additionally, during communication, users use various devices, and each communication involves transferring information between the nodes that make up the network. Messages may contain sensitive user data. Hence, there is a need to secure these data using cryptographic techniques such as encryption, hashing, security protocols, or authentication and key management algorithms [119; 120; 121]. While implementing security measures in the IoT systems, the so-called Cybersecurity triad (CIA triad) allows for managing the security policy in a computer network. The CIA triad oscillates around three aspects essential to securing communications. The first aspect is confidentiality, which ensures that there will be no unauthorized attempts to access confidential information. Integrity is the second aspect, providing data consistency, accuracy, and reliability. The last aspect is availability, which guarantees consistency and easy access to the data for authorized parties [122]. Thus, we should secure data transmission between devices using encryption protocols such as SSL/TLS to prepare an appropriately secured IoT network. Also, we should require strong authentication mechanisms for all devices to prevent unauthorized access, which means that only authorized devices will have access to the network. Next, we should use the principle of the least-privilege management model to mitigate potential risks. Thanks to this, we ensure that users have the appropriate permissions to access individual devices and data in the IoT network [123; 124]. IoT systems and WSNs are vulnerable to cyber attacks inside and outside the network. There are many classifications (e.g., routing-based, characteristic-based, based on the action layer of the communication protocol) and types of cyber attacks. A cyber attack may result in data loss, interception, or modification. The most-common attacks in these solutions are the Man In The Middle attack (MITM), stolen or guessing attacks, capture or impersonation attacks [125], zero-day attacks, malware [25], or (Distributed) Denial of Service attacks [126]. During the Man In The Middle attack, the aggressor tries to disrupt communication between two end systems by injecting a malicious node between legitimate nodes or attacking communication protocols in IoT systems. The duplicated packets can be sent multiple times to the recipient [125; 127]. In stolen or guessing attacks, the aggressor can guess the password when the smart card, device, or other verifier is lost or stolen from the server. After that, the aggressor uses the so-called offline password guessing technique due to the fixed verifier output value for the same input [125]. A capture attack refers to a sensor node or device. The aggressor hijacks such an element to take over the network. Next, he/she removes it from the network. During the last step of the capture attack, the aggressor redeploys the sensor node or device as a malicious node [125; 128]. Impersonation attacks refer to situations when the aggressor uses the identity of a different user, device, or another network element during communication. Also, the aggressor can install the client's certificate on such a device and next impersonate them [129]. The Denial of Service attack (DoS) consists of overloading the application serving specific data or handling customer data, i.e., exhausting its resources. If the aggressor uses computers in many places (called botnets [130]) during such an attack, he/she performs a Distributed Denial of Service attack (DDoS) [126; 131]. In zero-day attacks, the aggressor tries to use the vulnerability before software developers can find and fix it [132].