SAN FRANCISCO (CBS 5) ― "They identify your machine whenever you go somewhere... it knows that you've been there before," said Daniel Salazar of TechSavies.
He's talking about cookies -- special packets of information the websites you visit send to your computer to identify you and what you've done on that site.
Hundreds and hundreds could be stored on your computer.
Cookies do make your surfing easier, because sites you visit often can recognize you and tailor the site to you.
But cookies also give Google and the advertising company it bought, DoubleClick, information about your web surfing history.
"They may know more about you than some of your best friends," said Ryan Singel, a staff writer for Wired.com, "in that your best friends don't always know where you go on the Internet, your best friends don't know what you type into a search engine where you're talking about health problems... and you want some advice."
Cookies can stay on your computer for years, unless you delete them
