Tandem voted to block hostile takeovers.

The Cupertino, Calif.-based company said that, for each share of its stock, it will issue one right to buy a hundredth of a share of a newly created preferred stock for an exercise price of $80. The rights would be triggered when a person or group acquired 20% or more of Tandem’s common stock or announced or made a tender offer for 30% or more of the company’s outstanding shares. A shareholder could then exercise the right or wait for the merger to be completed, when the shareholder would get securities worth $160 in the surviving entity.