Oppenheimer & Co. controls 5.2% of Viacom stock.

The New York-based securities firm said in a filing with the Securities and Exchange Commission that it holds, or has options to buy, 1,784,500 shares of the entertainment firm, which has been the subject of heated takeover speculation. The shares were bought between Sept. 16 and Oct. 9 at prices ranging from $40.25 to $44.625 per share. The company’s board last Monday rejected a leveraged buyout offer from a management-led group at a price of $44 a share.