Websites need to generate revenue somehow, and the pressure to grow those numbers has never been greater. “Free” means you have give up something. It might be looking at advertisements. It may also be snippets of private information. Just like a puzzle, connect enough snippets and an identifiable picture can emerge.

Most of us have heard the stories of people losing jobs or worse over embarrassing photos they put on their MySpace pages. Of greater concern to individuals is that information shared on various social networking sites can potentially be combined. By identifying friends on Facebook or LinkedIn, pictures of yourself and family on Flickr, and using Twitter to communicate your movements and activities, researchers have found that it is possible to develop a far more detailed understanding of you and your habits than you would expect.

Maintaining privacy online is about to become way more complicated. There is a growing trend for websites to interconnect and share information about you with each other. For example, a recent new site called Blippy allows people to automatically share their credit card transactions as they happen. The problem is that it’s getting harder to recognize when it is happening, to monitor it, and to execute control over it.

A couple of years ago Facebook quietly turned on a feature called Beacon, which was positioned as a way to better target advertising. It turned out that it automatically opted everyone in and your activity and purchases at dozens of other partner websites was published in your news feed without your knowledge. Facebook quickly received a firestorm of criticism and eventually shut down Beacon.

Since then, Facebook has implemented Facebook Connect, a way to use your Facebook identity to login to other websites and share information with your friends. Now, Facebook is preparing to allow selected partners to access your profile unless you opt out or configure your settings properly.

Even Google has created controversy with “Buzz,” a recent feature added to Gmail. Buzz was supposed to be a way to share short messages with your friends, along the lines of Twitter. The problem was that they turned it on automatically for everyone, and the people you e-mail the most were revealed on your profile page. Google was forced to quickly change that.

As a result of these stories, I went through all the websites I maintain accounts with to find all the settings and configure them to ensure I was only showing, sharing or releasing the information I wanted. I found that it was complicated to understand what they were doing, that it was nearly impossible to visualize what was actually being shared and that it was difficult to even find all the actual controls that needed setting. It made setting up a home network seem simple.

This is confirmed by recent studies that found that the most popular and successful websites appeared to purposefully make privacy control challenging and that the default settings were usually configured to share the maximum amount of personal information.

Government and privacy watchdog groups are taking note and beginning to call for responsible action, but any real outcomes will likely take a long time to take effect. On the Web, things move rapidly and there is great momentum behind building and deploying these connections. So beware of unintended consequences — take a good, hard look at what you are sharing.

Roman Lubynsky is a technology consultant based in Boston. A frequent speaker and writer on technology topics, he has an MS in Management of Technology from MIT. Roman can be reached at roman@lubynsky.com.