Spyware is software that aims to gather information about a person or organization without their knowledge and gives the access to someone else.

(i) Virus : A computer virus is an executable software that spreads from one computer to another.

                           OR

A piece of code which is capable of copying itself and typically has a detrimental effect, such as corrupting the system or destroying data.

                           OR

Any other correct definition

(ii) Hacker : A hacker is an individual, who breaks security for non-malicious reasons to test the security of a system.

                            OR

A hacker practices to modify/alter computer software/hardware and informs the creator about the security issues.

(iii) Cracker : A cracker is a person who violates computer security for malicious intentions or for personal gain

A cracker is a person who violates computer security for malicious intentions or for personal gain

                           OR

A cracker practices to modify/alter computer software/hardware and uses it for personal gains/ to trouble the creator.