Perverse software:

Perverse software is a program which causes hindrances in other programs execution in such a way resulting in modification or complete destruction of data without the user's intention or even sabotaging the operational system.  Perverse Software is also known as Malicious software or malware.

It is a type of software that is designed to secretly access a computer system, without the owner's consent, and damage the system. The impact can be as damaging as shutting down a business, pulling down computer network or significantly impacting regular use of individual computer systems etc.

The damage done can vary from something as little as changing the author's name in a document to full control of one's machine without the ability to easily find out.   

Most malware requires the user to initiate its operation. For example, sending infectious attachments (it acts when users downloads them and runs the attachment) in e-mails, browsing a malicious website that installs software after the user clicks ok on a pop-up, and from vulnerabilities in the operating system.  

Early infectious programs, such as Internet Worm and MS DOS viruses, were written as experiments and were largely harmless or at most annoying. With the spread of broadband  Internet access, malicious software has been designed for a profit, for forced advertising. Here the malware keeps track of user's web browsing, and pushes related advertisements.