Hilton Hotels Corp. said it will buy back 3.9 million, or 15.6%, of its shares. At current prices, the buyback will cost Beverly Hills-based Hilton $234 million. Hilton's stock closed Monday at $60 per share, down $17.125 for the day amid Wall Street's steepest plunge in history. Hilton's price stood at $86.625 per share on Oct. 2. The company has 25 million shares outstanding. Hilton said it would repurchase the stock both on the open market and through private transactions, and it set no time limit on the buyback. The repurchased shares will be available for "various corporate purposes," the company said.