Nov. 6 (Bloomberg) -- The following companies are having unusual price changes in U.S. trading. Stock symbols are in parentheses, and share prices are as of 9:40 a.m. in New York.

Activision Blizzard Inc. (ATVI US) rose 11 percent to $12.21 and earlier climbed 13 percent for the biggest intraday gain since Oct. 13. The video-game maker formed in July when Vivendi SA bought a controlling stake in Activision Inc. said it plans to buy back as much as $1 billion of its stock.

Ambac Financial Group Inc. (ABK US) tumbled 10 percent to $1.80. A credit-rating downgrade of the bond insurance company that has slumped 93 percent this year forced it to post collateral and terminate contracts.

Amdocs Ltd. (DOX US) fell 20 percent to $18.90 and slid 21 percent earlier for the biggest intraday decline since June 2002. The world's largest billing and customer-service software provider reported fiscal fourth-quarter profit that fell short of the average analyst estimate and forecast first-quarter sales and earnings that trailed analysts' projections.

Blackstone Group LP (BX US) fell 8.1 percent to $7.90. The manager of the world's largest buyout fund said it had a third- quarter loss of $502.5 million as the financial crisis eroded the value of its private-equity investments. Blackstone had been expected to break even, based on the average estimate of seven analysts in a Bloomberg survey.

Continental Resources Inc. (CLR US) fell 10 percent to $26.20 and earlier slumped 13 percent for the biggest intraday retreat since Oct. 24. The U.S. oil and gas explorer reported third-quarter sales and profit that fell short of analyst estimates. Earnings of 62 cents a share were 19 percent lower than the average projection, according to Bloomberg data.

FTI Consulting Inc. (FCN US) tumbled the most since January 2004, losing 31 percent to $39.80. The company, which advises businesses on litigation, bankruptcies and restructuring, reduced its full-year earnings forecast and will delay an initial public offering of its technology business until next year.

Hertz Global Holdings Inc. (HTZ US) slid 17 percent to $5.54 and earlier fell as much as 23 percent, the most since Oct. 9. The second-largest U.S. rental-car company said third-quarter profit fell 89 percent as businesses and consumers cut back on travel. Hertz said it won't meet its 2008 earnings forecast.

Hot Topic Inc. (HOTT US) jumped 9.5 percent to $6.58 and earlier rose to $6.62, the highest in a week. The teen clothing and music retailer said in a statement of preliminary results that it earned as much as 17 cents a share in the fiscal third quarter, topping its previous estimate.

Las Vegas Sands Corp. (LVS US) tumbled 22 percent to $9.06 and earlier slid 33 percent for the biggest loss since its December 2004 initial public offering. The casino company whose shares fell as much as 95 percent from their October 2007 peak said it faces financing risks that may threaten its ability ``to continue as a going concern.'' The company registered with the U.S. Securities and Exchange Commission to sell an unspecified amount of securities.

McDermott International Inc. (MDR US) slumped 25 percent to $11.60 and earlier fell 29 percent, its biggest intraday drop in four years. The energy-services company that's expanding its nuclear-fuel business reported third-quarter profit that was 47 percent less than the average analyst estimate, according to Bloomberg data.

News Corp. (NWS/A US) fell the most in the Standard & Poor's 500 Index, dropping 13 percent to $8.56. The media company controlled by Rupert Murdoch said it expects fiscal 2009 profit to decline from a year ago, reversing its earlier projection for an increase of as much as 6 percent.

THQ Inc. (THQI US) dropped 28 percent to $4.73 and earlier fell to $4.37, the lowest since June 2000. The video-game publisher said it will close five studios and cut 250 jobs to reduce costs and focus on fewer, higher-quality titles. The company also lowered its sales and profit forecast for the fiscal year ending in March.

Toyota Motor Corp. American depositary receipts (TM US) fell 14 percent to $69.42 and earlier slumped 15 percent for the steepest decline in 18 years. The world's second-largest automaker forecast the biggest drop in profit in at least 18 years as a global slump cripples auto demand and gains in the yen erode the value of overseas sales.

Wal-Mart Stores Inc. (WMT US) rose the most in the Dow Jones Industrial Average, climbing 3.8 percent to $56.19. The world's largest retailer said October sales at stores open at least a year increased 2.4 percent, beating its own forecast.

Whole Foods Market Inc. (WFMI US) climbed 4.3 percent to $10.75 and earlier rose to $11.34, a two-week high. The largest natural-foods grocer said it received a $425 million equity investment from Leonard Green & Partners LP.

Yahoo! Inc. (YHOO US) jumped 4.9 percent to $14.60 and earlier rose to $14.89, the highest since Oct. 7. Chief Executive Officer Jerry Yang, coping with the cancellation of an advertising agreement with Google Inc. (GOOG US), said at a conference in San Francisco that he's open-minded about forging other deals.

To contact the reporter on this story: Elizabeth Stanton in New York at estanton@bloomberg.net

Last Updated: November 6, 2008 09:55 EST