Kevin Bankston of the Electronic Frontier Foundation recently said: "Google knows more about you than your mother." A few years ago, it might have sounded far-fetched.
But if you're one of the growing number of people who are using more and more products in Google's ever-expanding stable (at last count, I was using a dozen), you might wonder if he isn't on to something.
It's easy to understand why privacy advocates and policymakers are sounding alarms about online privacy in general - and singling out Google in particular. If you use Google's search engine, Google knows what you searched for as well as your activity on partner websites that use its ad services. If you use the Chrome browser, it may know every website you've typed into the address bar or 'Omnibox'.
It may have all of your email (Gmail), your appointments (Google Calendar) and even your last known location (Google Latitude). It may know what you're watching (YouTube) and whom you are calling. It may have transcripts of your telephone messages (Google Voice).
It may hold your photos in Picasa Web Albums, which includes face-recognition technology that can automatically identify you and your friends in new photos. And through Google Books, it may know what books you've read, what you annotated and how long you spent reading.
Technically, of course, Google doesn't know anything about you. But it stores tremendous amounts of data about you and your activities on its servers, from the content you create to the searches you perform, the websites you visit and the ads you click.
Google, says Bankston, "is expecting consumers to trust it with the closest thing to a printout of their brain that has ever existed".
How Google uses personal information is guided by three "bedrock principles", says Peter Fleischer, the company's global privacy counsel. "We don't sell it. We don't collect it without permission. We don't use it to serve ads without permission." But what constitutes "personal information" has not been universally agreed upon.
Google isn't the only company to follow this business model. "Online tools really aren't free. We pay for them with micropayments of personal information," says Greg Conti, a professor at the US Military Academy at West Point and author of the book Googling Security: How Much Does Google Know About You? But Google may have the biggest collection of data about individuals, the content they create and what they do online.
It is the breathtaking scope of data under Google's control, generated by an expanding list of products and services, that has put the company at the center of the online privacy debate. According to Pam Dixon, executive director at the World Privacy Forum, "No company has ever had this much consumer data" - an assertion that Google disputes.
Opacity versus transparency
Critics say Google has been too vague in explaining how it uses the data it collects, how it shares information among its services and with its advertisers, how it protects that data, and how long it retains that data before deleting or "anonymising" it so that it can't be tracked back to individual users.
"Because of Google's opacity as to how it is using that data, and a lack of fundamental information rights [that] users have, [privacy] becomes a very thorny question," says Dixon.