Spyware is a type of malicious software, or malware, that is installed on a computing device without the end users knowledge. It gathers data about the device and user and sends it to third parties without their consent. Spyware can also refer to legitimate software that monitors data for commercial purposes like advertising. However, malicious spyware is explicitly used to profit from stolen data. Spyware can steal sensitive information and internet usage data and relay it to advertisers, data firms, or external users. It can also track login credentials and spy on sensitive information. Spyware can make its way onto a device without the end users knowledge via an app install package, file attachment, or malicious website. Some of the most commonly used types of spyware include adware and infostealer. Signs of a spyware infection can include unwanted behaviors and degradation of system performance.