## 1 Introduction  
An exponential increase has been noticed in the number of Internet users since the last decade. Latest data reveal that there were 5.098 billion Internet users in December 2020, which equals to 64.7% of the population on the earth [1]. Consequently, the Internet is the most popular medium to connect globally and the largest knowledge repository available. It facilitates communication via different techniques such as text, video or audio, therefore making a lot of private user information available on various platforms. The introduction of IoT technology with a combination of advanced network technology has become an integrated part of humankind. The devices include smart home appliances, smart grids. These also act as building blocks of the vision for smart cities. Usage of these devices support continuous data transfer without any human intervention [2]. This has created an exponential rise in the IoT industry. A report on IoT analytics indicates that the number of IoT devices is expected to surpass 35 billion by 2025, whereas 22 billion devices were already connected in 2018 [3]. This increase corresponds to the fact that the IoT is extensively leveraged to solve problems in various domains such as smart cities, garbage management system, smart traffic management system, water supply and monitoring air standards to control pollution [4]. An IoT-based development can be seen in smart home automation appliances, smart cars, industrial M-to-M communication and robotic surveillance in the military [4,5]. Pertaining to these applications of the IoT in various domains, there is a huge amount of data transfer. This makes the devices susceptible to intrusions, as cyber criminals often try to gain control in illicit ways. The end goal of intrusions is to access a user's confidential information. Cyber criminals manipulate confidential information to gain remote access to the devices [6]. This may pave the way for intruders to perform illegal activities using a fake identity and possibly financial loss [7]. Some of the frequent techniques employed by intruders are discussed below:  
1. _Malware_--malware is just code packed with malicious content. About 92% of malware is deployed via email attachments and the rest as downloadable content. The primary motivation of using malware is to infect the device and steal or destroy information. In November 2020 alone, about 113 million new malware programs were reported [8]. 2. _Phishing_--it simply is an act of posing as a legitimate organization or person and asking users for sensitive information. According to the APWG report in the Q4 of 2020, 22.5% of the phishing activities targeted financial institutions, 22% of them involved SAAS/webmail and 15.2% of them were involved in payment activities [9]. 3. _Password attack_--these include frequent dictionary attacks or keyloggers to gain access to users' passwords. Password decryption is employed to gain the original password from the hashed password. Therefore, it is essential to have a password combination consisting of alphabets, numeric and special characters. 4. _DDoS_--a distributed denial-of-service interrupts the proper functioning of Internet-connected devices. It continuously sends fake requests to the server, consequently increasing the load on the server. Hence, when a legitimate user sends a request to the server, the server is not able to respond to valid requests. If the same activity is performed by a large number of infected devices, from which millions of requests are sent to the server and if a valid user tries to request on the server, the server is unable to respond due to high traffic or malicious requests. In a report by Netscout, 929,000 DDoS attacks were recorded within 31 days, in April-May 2020 [10]. The statistics suggest an increasing number of intrusion attacks. These attacks are successful due to a lack of awareness and proper knowledge [11].