That's because one version of Google's toolbar keeps track of every site a person visits to analyze search and surfing patterns.
"By using the Advanced Features version of the Google Toolbar, you may be sending information about the sites you visit to Google," the company warns during the Toolbar installation process. "In order to show you more information about a site, the Google Toolbar has to tell us what site you're visiting which it does by sending us the URL."
Google launched its new toolbar Monday just as privacy advocates are calling attention to the potential hazard of free software extensions, some of which collect more personal information than people who download them may realize.
Google goes out of its way to inform people that the toolbar will track where they surf, earning it plaudits from at least one privacy advocate who suggested that the company had cleared crucial hurdles by disclosing its intentions and making the results anonymous.
But he also raised concerns about Google's anonymous dossiers, suggesting that any collection of data tied to a single copy of the toolbar runs the risk of one day being identified with a single person.
"If they're storing any unique identifier associated with any particular install, that raises the possibility of subsequent identification," said Jason Catlett, president of Junkbusters. "If they have, that should be disclosed. If they are storing a permanent history of the URLs on this server with that unique ID, that becomes more of a privacy risk."
Google acknowledged that the toolbar created unique files and said people should trust that the company will maintain its policy of keeping those files anonymous.
"Google bends over backwards to make the user understand what's going on," said Google spokesman David Krane. "We're looking at data en masse, not going record by record. It's very much the 50,000-foot view, rather than searching for personal information."
Krane noted that Google is taking extra care not to collect URLs that include information about the visitor--a practice that has landed others in hot water.
Alexa Internet has earned parent company Amazon.com complaints and several privacy lawsuits alleging that Alexa's collection of these types of URLs--which can include anything from a person's name to a physical address--violated privacy law.
Alexa's technology provides a list of Web sites related to the one a person visited.
Google also promises not to give the information it gleans from the tracking to third parties.
Krane said the company will use the information for internal purposes only, with the specific purpose of refining its search engine generally and the toolbar in particular.
The toolbar feature in question extends a technology already used on the Google search site to a person's travels throughout the Web. The patent-pending technology, PageRank, is Google's method of rating the importance of Web pages by counting the number of other Web pages that link to them.
Based on traditional citation analysis, PageRank has made the search provider an instant hit on the Web, earning it the Yahoo contract, a wide audience, and the keen interest of venture capitalists. In last year's funding round, led by Sequoia Capital and Kleiner Perkins Caufield & Byers, the search start-up raised $25 million.
The rating feature is one of several included in the toolbar. Others include the ability to search specific Web sites or individual pages and to highlight different found search terms in different colors. The toolbar is also taking a page from the troubled Alexa effort, providing lists of related pages.