Editor's note: Marc Rotenberg is president of the Electronic Privacy Information Center, a public interest research center in Washington. He teaches law at Georgetown University.
(CNN) -- Back in 2010, Google launched a short-lived social network service called "Buzz." Instead of simply promoting Buzz and urging users to sign up for it, or opt in, Google chose instead to sign up Gmail users as Buzz users. If users weren't happy, they could always opt out.
It was a mess. Private e-mail addresses became publicly available as social network contacts. Users rebelled. The Federal Trade Commission investigated, Google backed off, and eventually the company settled with the FTC and agreed not to rope users into new services that they haven't signed up for.
Now Google is back at it.
This week the company announced that it was tying the inboxes of Gmail users to Google+ users. By using Gmail addresses to autocomplete messages from Google+ users, Google is basically giving strangers who may not know your e-mail address a way to connect with you through Gmail. This move may bolster short-term value for Google but reduces privacy for Gmail users.
The consequences for users and for the Internet are troubling. From a privacy perspective, Google's action makes it more likely that personal information of users will become more widely available. And as the Internet's most dominant company, Google is exploiting its control over key Internet services to beat back competition and expand its market reach. Those who favor a free, open and democratic Internet should take note.
Google is also unfairly expecting Gmail users to opt out of a service they never signed up for to maintain their current expectations of privacy.
It's fine if some users like the new feature. They should be free to opt in. But those who value privacy should not be expected to check their privacy settings every time a company alters its business model.
With the latest change to Gmail, Google is testing the resolve of regulators to protect privacy. If government officials do not intervene, things could get much worse.
At the moment, Google is simply using Gmail account addresses to auto-complete e-mail addresses for Google+. But of course Google is sitting on the biggest search database in the world and could also use that data it has collected from users to auto-complete e-mail addresses and much more.
In 2010, Google was right to back off the plan for Buzz and the Federal Trade Commission was right to pursue an investigation and help ensure that similar fiascos do not occur. But now that Google is once again commingling data in e-mail accounts and social network accounts, the Federal Trade Commission will need to intervene. Opting out is not the solution.
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The opinions expressed in this commentary are solely those of Marc Rotenberg.