Spyware is a type of malicious software -- or malware -- that is installed on a computing device without the end user's knowledge. It invades the device, steals sensitive information and internet usage data, and relays it to advertisers, data firms or external users.
Any software can be classified as spyware if it is downloaded without the user's authorization. Spyware is controversial because, even when it is installed for relatively innocuous reasons, it can violate the end user's privacy and has the potential to be abused.
Spyware is most commonly distributed by getting potential victims to click on a link. The link can be in an email, pop-up window or ad. Malicious code can also be embedded on legitimate websites as an advertisement. Other ways for spyware to infect a machine include via drive-by download -- where spyware is downloaded just by visiting a website or viewing a HyperText Markup Language email message -- phishing links or physical devices.
Spyware is one of the most common threats to internet users. Once installed, it monitors internet activity, tracks login credentials and spies on sensitive information. The primary goal of spyware is usually to obtain credit card numbers, banking information and passwords.
