With around 90% of computers connected to the internet being infected with spyware, there is no doubt that this is a major problem.
Spyware has the ability to display advertisements and tinker with personal settings, which is a major annoyance to many people, and causes millions of machines to run slow.
You may wonder, why would anyone want to infect people with spyware? Well, as you may guess, the reason is mostly to make money off each computer infected.
Originally, computer viruses were made mostly as a joke or a prank, and had no commercial application (the first computer worm in the late 1980's targeted NASA and had the sole aim of slowing down their system).
As more people started using the Internet, however, unethical companies who realized there was money to be made began to distribute spyware for profit.
Companies like this make money off their creations in a number of ways.
First and foremost, adware will bombard you with advertisements (often with general offers such as relationships and fitness).
Advertisers sign up and pay a set fee to the company distributing the software for every thousand people who see their advertisement.
With malicious software often showing ads every minute, the impressions can add up fast, and over a long period of time can result in a significant amount of advertising revenue for the unethical company infecting people with their software.
Other than pop-up advertisements, these companies do a number of other things to profit off each infected machine.
A common thing is to change your homepage.
That way, every time you open your web-browser, you are exposed to an advertising message.
In addition, harmful programs will often insert a tool bar on your internet explorer browser with additional advertising.
Many programs even remove all existing tool bars you have installed in order to make way for the new tool bar they install with advertising.
Additional things programs like this can do is drop icons on your desktop (often linking to more advertised websites) and add favorites to your favorites menu.
You may end up having more programs open when you start up your computer, and these things, combined with toolbars and your changed homepage, allow the company distributing spyware to bombard you with as many advertisements as they feel like.
Considering how difficult software like this can be to remove, the unethical company can end up making a lot of money over a period of time.
How much companies who make spyware end up making is never actually revealed, and are typically shrouded in secrecy.
If you ever feel like starting a business, however, just remember that there are better ways to make a living than infecting people with adware.