Is There Such a Thing as Internet Privacy?

Internet spying has become big business, "more pervasive and far more intrusive" than all but a few people know. That's from an extensive study by the Wall Street Journal, which reports that companies track users in real time so they can advertise instantly. They can learn all about you — not just your shopping interests, but your financial and medical conditions — even what you're telling your friends on social networks. Are there benefits for consumers?  What are the prospects for abuse?  Is there any way to opt out?  Would new government rules make a difference?