The first patch fixed a vulnerability in handling long file names, called the SaveAs vulnerability, and the second a vulnerability in dealing with the Web site addresses displayed in Chrome's status area when the user hovers over a link.

Larson also established a Google Chrome Releases blog for announcements and release notes relating to Chrome. The company had said earlier it was working on a way to release that information, in part after people requested such notes well after Google started automatically updating Chrome browsers without saying what exactly was in the update.

Google fixed two lesser security issues, too. First was an issue in which typing "about:%" in the address bar could crash the computer. The problem also meant that a Web page with that text as a hyperlink could crash the browser if a user hovered the mouse pointer over the link. Second was to prevent the user's desktop from being the default download directory to mitigate "the risk of malicious cluttering of the desktop with unwanted downloads, which can lead to executing unwanted files," Larson said.

Other fixes addressed non-security issues: a JavaScript problem with Facebook; a problem suggesting search terms while using various Web sites; and some data-transfer issues with the Safe Browsing mode.

The Justice Department has quietly hired one of the nation's best-known litigators, former Walt Disney Co. vice chairman Sanford Litvack, for a possible antitrust challenge to Google Inc.'s growing power in advertising.

Mr. Litvack's hiring is the strongest signal yet that the U.S. is preparing to take court action against Google and its search-advertising deal with Yahoo Inc. The two companies combined would account for more than 80% of U.S. online-search ads.

In 4 p.m. trading on the Nasdaq Stock Market, Google shares had tumbled 5.5%, or $24.30, to $419.95, while Yahoo shares were up 18 cents to $18.26.

For weeks, U.S. lawyers have been deposing witnesses and issuing subpoenas for documents to support a challenge to the deal, lawyers close to the review said. Such efforts don't always mean a case will be brought, however.

It isn't clear whether a U.S. challenge would target the Google-Yahoo deal alone or take on broader aspects of Google's conduct in the growing online-advertising business.

It is relatively rare for the Justice Department to hire a special counsel from outside the department. David Boies was brought in as a special counsel to build the landmark antitrust case against Microsoft in 1998, and Stephen Axinn, another well-known New York litigator, was hired to challenge Worldcom Inc.'s proposed buyout of Sprint Corp.