In the simplest terms, spyware is any software that monitors your computer covertly and transmits the data it collects to someone else. In fact, companies and organizations sometimes install spyware deliberately. Some employers, for instance, use it to monitor what their employees are up to.

The four common types of spyware are adware, Trojans, internet tracking, and system monitors. Their function ranges from tracking your browser activity so marketers can target your interests, for instance, to monitoring your keystrokes and nearly everything you do on your device.