Spyware is dangerous application or code that is written specifically to steal the user's information like credit card details, social security number, passwords, or similar information or to spy on the user's online behaviour. Spyware is generally written so that it installs itself without the computer user's knowledge and in most cases the user may not be even aware about the fact that his/her online activities are being observed. Many spyware can also hijack browser settings, display unnecessary popups and download and install software, computer viruses or other spyware. Spyware deletion can be sometimes challenging because they are often concealed to the user.

At first the word "spyware" applied to computer hardware that was meant for espionage purposes. However, after being mentioned in a press release in late 2000 by Gregor Freud, the founder of Zone Labs, the word has taken on its present meaning. Today, almost everyone who is familiar with computers and the World Wide Web might be aware of virus programs, spyware applications and other malware.

Spyware applications generally install themselves by utilizing vulnerabilities in the computer software or when the computer user unknowingly installs infected or "tagged" files from removable media. The main difference between viruses and spyware is that unlike virus applications, spyware programs do not replicate i.e. make exact copies of themselves and infest other systems. Some trojans also install spyware or other malware without the user's consent.

Microsoft Windows is more vulnerable to spyware programs and other such malware programs. Apple's MacOS X and other OSes like GNU/Linux and FreeBSD derivatives are less vulnerable compared to Windows Xp. There is a lot of debating on why there are less number of spyware applications aimed at GNU/linux and PCBSD. Many security experts claim that these operating systems are inherently much more secure and it is problematic to code spyware to run on these platforms. Other experts claim that since the use of these OSes is way lower when compared to Windows, spyware developers don't think that it is worthwhile to develop spyware applications specifically for these platforms.

If you use a Windows computer, it is recommended to daily apply updates to your OS to stay protected from spyware. Update files contain rectifications and patches to security loopholes. It is also suggested to install and use another browser like Firefox or Opera instead of the default browser-Internet explorer. These browsers are more safe and can help in keeping your computer safe from spyware.

You should also download and install a effective virus remover and update it regularly. Most good anti-virus software can delete spyware. However, you can also install an anti-spyware software in addition to anti-virus software for maximum benefit. A firewall software is also recommended. Many anti-virus applications or Internet security suites, as they are called, have a firewall as well.