A computer virus is a man-made malicious software program that is loaded into a computer system without the user's knowledge and performs malicious actions. It can infect your computer,software, servers and many other things. It is a type of malware.When a virus infects the host system, then it can also infect other computers on the same network. It can modify or disable very important functions or applications. It can also copy, delete or encrypt your data. Some viruses start replicating as soon as they infect the host while some viruses stay inactive until they receive a specific signal to trigger them. Virus is designed to replicate and spread.It usually spread in one of four ways.

• Removable Devices such as Universal Serial Bus (USB).
• Downloads infected files from the Internet.
• Email attachments.
• Viewing infected website advertisements, known as malvertising.

Ransomware is a form of malicious software that locks the user out of their files or their system and then   demands a ransom (payment) to restore access. Ransomware attackers hit businesses, organizations, and individuals alike. If the victim paid the ransom then also it might not get access to his/her system. It comes into your system when you mistakenly download malware through email attachments or links from unknown sources.

Hacking involves cracking systems or networks to gain unauthorized access to the data stored in them. The person who is involved in these acts is known as a hacker. They performed these malicious acts for financial gain, protests, spying etc... The most common hacking techniques that hackers use are Botnets, Browser hijacks, Ransomware, Rootkits, Trojans. Poor web configurations, old software, inactive or disabled security controls and weak passwords are some examples of areas that make computer networks and systems vulnerable to attacks.
Hackers are classified into various categories.

The word vandalism refers to destruction of anything important. It is an illegal act of damaging digital data, rather than stealing and misusing it. Website defacement, malware that erases data, brandjacking etc... All these act falls under cyber vandalism. The main motive behind cyber vandalism is maligning the image or reputation of a business house. It could negatively impact business, brands and their goodwill. Those who create mallware to damage electronic files are known as cyber vandals. They also create elements that can disable your data,networks or even your computer systems.

Cybersquatting is an act of registering, selling or using a domain name that is intentionally named almost identical to an already existing popular trademark name belonging to someone else. It is also known as domain squatting. It is carry out against business houses that have a large web presence. The person who involved in these act are known as cybersquatters. These domain names are created to make huge profit by diverting audience to the cybersquatters' site.

Cyberterrorism is the use of the Internet to conduct violent acts that result in, or threaten, the loss of life or significant bodily harm, to achieve political or ideological gains through threat or intimidation. It mainly occurs against organisations, business houses, and even against government establishments. It is used to generate fear and violence that results in the loss of critical infrastructure. It is conducted by manipulating computer systems. Most of the time, these attacks are anonymous and carry out from many miles away from the target. This makes them difficult to track.