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As the name suggests, this type of cookie is saved on your computer so that when you close it down and start it up again, it can still be there.
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Analytics cookies are probably the most common form of persistent cookies in use today.
However, persistent cookies can also , oddly, have a shorter life span than some session cookies, as they can be coded to be destroyed within a second or two of being set, whereas a session cookie will always last until you close down your browser.