An unsettling reality has begun to descend on the millions of fans and devotees of the Internet giants Google and Yahoo: They know an awful lot about us.

Every Google search ever typed, every Yahoo news article ever read -- all are logged and stored indefinitely in these companies' massive databases. Think about that for a moment. We whisper a lot into the ears of these shadowy search engines, including plenty of secrets that we'd want to keep from our spouses and kids. And we do so without ever bothering to check what is being done with that information.If you don't already know, let me be the first to tell you: Google, Yahoo and their less-well-known brethren are keeping tabs on what is being searched, viewed and clicked on, all across their sprawling Web empires.

You know all those e-mails you've sent using free services such as Yahoo Mail or Google's Gmail? They are kept for posterity on company servers, even in cases when they have been deleted from users' accounts. And instant messages? A new service from Google leaves a digital record long after the conversations have been forgotten. Driving directions? Not only do Google and Yahoo know the way to our intended destination, they also know that we probably made the trip. (We all but told them we were going, didn't we?)

Searches are not by default linked to our names -- only to an Internet address or a unique browser ID. But armed with that information, investigators and sometimes the companies themselves can make the crucial link to our names and addresses.

Existing laws offer fewer protections for data and e-mail communications stored by a third party than for the contents of someone's personal computer. And though there are gray areas in the law, this much is clear: plenty of what the search engines have amassed about us may be obtained without a wiretap or search warrant.