The Internet has become not only a primary means of communication but a place where millions of Americans store important personal data, from credit-card numbers and bank account information to family photos and histories of their online purchases. But that data does not have the same legal protection as data that Americans store in their homes. What's more, powerful new technologies are creating unexpected challenges to privacy online. Advertisers, for example, can now track the Web sites you visit, and actions you take on those sites, to analyze how to more effectively sell products to you. And they may sell the information they collect to others. Privacy advocates, and some lawmakers in Congress, say the growing threats to online privacy point to the need for stronger laws to protect users' data. But Republicans in Congress warn that overregulation may cripple the economic foundation of the Internet.