However, the Web History service can be of value to individual users, not just to Google. A searchable history of every Web search you've ever run could be a powerful tool for your own use. If you're comfortable with your search data being available in Web History but want to prune a few "incriminating" searches from the list, choose Web History under My Products from your Accounts page and click "Remove Items" in the left-hand menu. This will place a checkbox next to each query in your history; select the ones you want to chuck into the Memory Hole and click "Remove," and they'll be deleted.
You can also click the "Clear entire Web history" link at the bottom of the page to delete your past searches all at once, or "pause" Web History for a while, if you know some of your upcoming searches might be difficult to explain or reveal too much personal information. To put Web History on hold, just click the "Pause" link in the left menu, then click "Resume" to have Web History begin saving your searches again.
Logging out of Google prevents the direct association of searches with you, but not the searches' association with your IP address and other information such as the operating system and browser used, time and date of the search, and the ID of the cookie saved to your computer for that search. (Google's Privacy FAQ shows a sample log entry.) A determined attacker could conceivably work backward from Google's server logs to discover your identity.
To prevent this, anonymize your Web use by using tools like Tor, Anonymizer or the PhZilla Firefox extension. These tools funnel your Web use through one or more proxies, bouncing from city to city around the world, so your searches cannot be traced directly back to your computer. Be warned, though: Internet surfing is significantly slower when it takes place behind a proxy server.
Risk 2: Tracking cookies
Use your browser's security or privacy settings to reject third-party cookies -- that is, cookies that originate from sources other than the site you're on.
Blocking all cookies can be problematic if you want specific sites to remember your log-in info or preferences. Blocking third-party cookies, on the other hand, won't inconvenience you on most sites but will take your privacy up a notch.