LOS ANGELES — Without letting you know, your Internet browser gulps down hundreds of digital tracking beacons known as cookies fed to it by the websites you visit, sometimes storing them for months or years, enabling an array of companies you’ve never heard of to monitor what you do online.
Cookies are not inherently dangerous — they are a kind of virtual ID card that helps browsers perform a number of online tasks that most users have come to expect: allowing you to stay logged in to your Google or Yahoo e-mail service, or to go from page to page on Amazon .com while filling up your shopping basket with books.
But the useful cookies are far outnumbered by those that serve no other purpose than to keep track of what you do online. They often come from sites you have never visited. This can happen when you open pages that carry embedded advertisements, which are capable of adding cookies to your browser without your permission or knowledge — and often do.
These tracking cookies allow ad firms to follow you from site to site. Over time, the trail of sites you visit may allow them to build a demographic profile about you that includes your hobbies, place of residence, income and even health status.
To get a sense of how many ad companies have cookies on your computer, go to the Network Advertising Initiative’s website. When you click on “Consumer Opt Out,” the NAI will show you which of its member companies have tracking cookies on your browser and give you the chance to opt out of tracking by those companies.
