Just about every piece of information about you has value: which soft drink you buy, what kind of car you drive, your income bracket, your medical information, your musical tastes and even what kind of mood you're in today.
Some of this information is useful for:
- Making the service better for you.
- Selling you products or services.
- Scoping out the user demographics of sites, again with the goal of designing and targeting products or services more successfully to consumers.
- Employers or insurers who want to check your background or search your medical history, for example. They may search (or hire a company to search) for your information, unbeknownst to you.
Some people feel that more targeted advertising simply makes sense — you avoid seeing ads for things that are useless or even offensive to you. But there's also the seedy side of the Internet, which includes criminals who compile catalogs of information about people who just bought expensive electronics. They can sell this information to thieves.