What is spyware?
Spyware is like a virus in that it is an unwanted program that runs on your computer. However, it does not try to replicate itself to other machines.
Infection usually occurs when it is installed alongside another program such as a peer to peer file sharing application. However, increasingly, spyware is blending with viruses making it harder to eradicate and harder to avoid.
There are different types of spyware. At one end of the spectrum, adware is designed to get you to visit commercial websites, typically for gambling and porn. It can, for example:
Pop-up unwanted adverts, including offensive material.
Download adverts from the internet, taking up your bandwidth.
Hijack your browser so that new menus appear or your default home page or search page is changed.
Put new icons on your desktop.
More sinister versions of adware will:
Block access to certain websites.
Try to get you to shut down anti-virus or anti-spyware defences.
Block updates to these defences.
Be extremely hard or impossible to remove.
Track your online activities in an effort to send you more adverts.
Surveillance spyware is the most extreme version. In common with some viruses, spyware can:
Scan your hard disk for private data such as credit card numbers.
Log the keys you type scanning for passwords or credit card numbers.
Take screen shots of the sites you visit to capture personal information.
Upload this information to criminals over the internet.
The whole point of spying on people is to remain undetected. The very worst kinds of spyware tend to operate in stealth mode and you may not even know you have them.
It is not uncommon for unprotected PCs to have several different types of spyware running simultaneously.
Often spyware applications are badly written and interfere with the computer's operating system, making the computer slow or prone to crashing.