It has become a maxim in the digital world: If you're getting something for free online, you're not the customer -- you're the product.
The point is that those providing whatever service you are using probably are collecting marketing information about you that they're likely selling.
It's a transaction that countless Americans are willing to engage in. But there must be limits to data mining, and people should have clear explanations of what personal data is being collected and uncomplicated ways of opting out.
A California court case over Google's practice of mechanically scanning e-mail content in order to create user profiles has brought these issues into sharp focus.
A federal judge recently found Google might have violated wiretap laws by perusing e-mails of those who send messages to Gmail accounts but are not customers.
"Accordingly, the statutory scheme suggests that Congress did not intend to allow electronic communication service providers unlimited leeway to engage in any interception that would benefit their business models," Koh wrote.
The case raises broader privacy concerns. Ordinary Americans should know that it's not just the National Security Agency that is collecting data about them.
Marketers are amassing vast troves of data about online users. The New York Times reported earlier this year that the number of companies collecting "information about the reading habits, health concerns, financial capacity, search queries, purchasing patterns and other activities of online consumers has skyrocketed."
Marketers argue it enables companies to show Internet users ads that are relevant to their lives. Opponents call the online tracking an invasion of privacy that isn't as anonymous as proponents claim.
Sen. Jay Rockefeller, D-W. Va., is among the federal lawmakers concerned about the situation. Earlier this year, he reintroducted his Do Not Track Online Act, which gives consumers the power to prevent the collection and sale of their data.
It contains privacy protections worthy of consideration.
While the advertising industry has made efforts to regulate itself in this regard, the value of these programs is debatable.
As online marketers become more sophisticated about the ways in which they compile information about Internet users, so too should the efforts to ensure they don't violate privacy boundaries.