Your search history contains some of the most personal information you will ever reveal online: your health, mental state, interests, travel locations, fears and shopping habits.
Unfortunately, your Web searches are carefully tracked and saved in databases, where the information can be used for almost anything, including highly targeted advertising and price discrimination based on your data profile.
"Nobody understands the long-term impact of this data collection," said Casey Oppenheim, co-founder of Disconnect, a company that helps keep people anonymous online.
Fortunately, Google, Microsoft's Bing and smaller companies provide ways to delete a search history or avoid leaving one.
Google makes it easy to find your personal Web history, manage it and even delete it. Just go to http://google.com/history and log in to your Google account. There, you will see your entire history and can browse it by category. If you would like this history to go away, click the gear icon in the upper right of the page and choose Settings. Here, you can turn off search history, so Google won't save future searches. You can delete your history from Google's database or just remove specific items from your recent history.
This does not opt you out of ad tracking, however. It just gets rid of a potentially embarrassing or damaging historical record. Google also lets you opt out of targeted and search ads on the Web and in Gmail, at http://google.com/settings/ads.
You can turn off and erase your search history on Microsoft Bing at https://www.bing.com/profile/history. Yahoo lets you turn off future search histories but doesn't have a way to delete the old one. Visit http://search.yahoo.com/preferences/ to turn off your history.
Even with your history turned off, though, you are still sending a lot of personal data when you surf or search from all three, especially if you are logged in to your Google, Microsoft or Yahoo account when you search.
DuckDuckGo collects no personally identifying information (like your IP address) as you search and doesn't save any search history that can be tied to you. But DuckDuckGo still makes money on ads.
Other options include PrivateLee, Qrobe.it and IxQuick, which is based in the Netherlands.
If you are partial to Google, Bing or Yahoo as a search engine but want it to be anonymous, try Disconnect Search.
The Web version lets you specify Google, Bing, Yahoo, DuckDuckGo or Blekko as your engine, but it searches them without sharing your Internet address or saving a search history.
You can also install Disconnect Search as a plug-in for the Chrome or Firefox browsers, so you don't have to remember to go to the site.