## 4 Devices' Vulnerabilities and Requirements
### Classification of IoT Security Attacks on Different Layers of IoT Networks
#### 4.6.4 Application Attacks or Software Attacks  
Software or application is the fourth factor that increases the danger of IoT security. Malware is introduced into the network's application to start this attack. This malicious program can disrupt and monitor operations, spread viruses, corrupt or steal data, and more. * Virus and Worms: A virus is a small, self-contained computer software that can replicate and infect other computers in the same way that a real virus can. A virus is just one sort of \"malicious logic\" that can maltreat an IoT network. A computer worm is similar to a virus in that it spreads by itself rather than being disguised inside another software [170]. * Malicious Scripts: Usually, there is an internet connection in the IoT network. In this attack, an attacker fools the user, who controls the gateway, by visiting lucrative advertisements or websites and then running executable active-x scripts with malicious alterations to different parts of the system, which could lead to the system being shut down or data being stolen [171; 172]. * Spyware and Adware: To propagate malware and harmful code, adversary attacks devices, such as IoT, use factory default user credentials, password brute-forcing, breaches, and manipulating weak configurations. Once the attacker has complete control, he can launch a DDoS assault against a target. A malicious party could insert harmful software into the system, which can result in data theft, data tampering, or even a denial of service [173]. * Trojan Horse: A Trojan Horse camouflage is a legitimate program where some previously defined event or date is present. This attack is triggered in the pre-set condition and then delivers a payload that may completely shut down the system [174]. * Denial of Service: An attacker can use distributed DDoS and DoS attacks to prevent users from accessing a system or network resource. This attack undermines the network or systems' capacity to perform expected functions. This attack comes from numerous points, and it is difficult to defend against this attack [175]. * Distributed Reflection Denial of Service Attack (DRDoS): DRDoS is one form of DDoS attack. In this attack, an attacker preserves anonymity through an IP address by using a third party, called a reflector, which needs not be compromised [176]. Numerous victim machines that unintentionally take part in a DDoS attack on the attacker's target are typically used in DRDoS attacks. Requests sent to the victim host computers are reflected back to the target from the victim hosts. The attacker sets the target's IP address as the source IP address to the reflectors to flood the network with response packets. They typically also generate an increased volume of attack traffic [177]. The advantage of the attack is that the attacker's identity will not be revealed as the attack will be done by reflectors, not by the attacker, which makes it hard to identify the original attacker and block the service. Another benefit of the DRDoS attack strategy is amplification. An attacker's first request results in a response that is greater than what was sent when there are numerous victim servers involved. This increases the attack bandwidth and the likelihood that a denial of service outage will result from the attack. DNS, NTP, SNMP, and SSDP are the protocols for UDP-based DRDoS attacks; SYN and BGP are the protocols for TCP-based DRDoS attacks [178]. Firewalls, intrusion detection systems, machine learning, etc. can be used to mitigate DRDoS attacks [179]. * Firmware Hijacking: Hardware's fundamental component is firmware. Every piece of hardware on a computer has this basic software preinstalled. Firmware modification or hijacking attack is one of the most catastrophic attacks where attackers can gain control of the entire system. It has already impacted various embedded systems such as telecommunication infrastructure, SCADA, and PLC systems [180]. * Botnet Attack: The botnet is a phrase derived from the concept of bot networks, where a bot is a computer program or robot that is automated.