A persistent cookie is a cookie that is stored on a computer indefinitely so that the site can identify the user during subsequent visits. The intended use of a persistent cookie is to record user preferences for a single website so that the site can automatically customize its appearance or behavior for the user's future visits. In this way, persistent cookies can help websites serve their users more effectively.
Unfortunately, persistent cookies also can be misused as spyware to track a user's Web browsing activities for questionable reasons without the user's knowledge or consent. For example, a marketing firm could place advertisements on many websites and use a single cookie on a user's computer to track the user's activity on all of those websites, creating a detailed profile of the user's behavior.