The words we type into Google may seem anonymous and innocuous at the instant we're doing a search, almost as if we are confessing to some digital high priest: "Lord, just between you and me, I am fascinated with . . . recreational drugs, bondage, Islamic radicalism, how to cheat my friends at poker. . . . " But our inquiries leave behind permanent tracks that could come back to haunt someday.

Consider for a moment what a complete history of just your Internet searches alone might reveal. Chances are the list would offer pretty good clues as to your political leanings, your health condition, your finances, your job satisfaction, your marital fidelity, your obsessions and addictions, and plenty else that you may want to keep private.

Add to that the full archive of your Web e-mails -- and depending on what other Yahoo or Google services you use, a partial or full record of your Web surfing habits -- and these companies have got a fairly comprehensive digital dossier on you, me and several hundred million other people.

This is a treasure trove by any accounting, and potentially a very valuable, perfectly legitimate asset to criminal and terrorism investigations. But such an accumulation of personal data also presents a tempting target for intrusive fishing expeditions by law enforcement, divorce lawyers, government prosecutors and even less savory characters.

What's more, the whereabouts of this data are generally kept secret. The records are sequestered in undisclosed locations, entirely out of our control, and may even be stored in a country other than the one in which a user lives, raising potential legal complications.

In China, both companies have come under fire for complying with the communist regime's censoring of the Internet. Yahoo has twice turned over personally identifying information about Chinese dissidents that led to their being jailed.

Here in the United States, the search engines say they comply with legal requests for information, but they rarely comment on the extent of their cooperation in handing over search data for criminal or civil cases. (In at least one case, a person's search history was used in prosecution, but that information was skimmed from his own computer.) Nevertheless, unless laws are rewritten or company policies changed, the search engines will find themselves increasingly bombarded with subpoenas for their users' search histories.