By Cliff Edwards, Bloomberg News

SAN FRANCISCO — Netflix Inc., the world’s largest subscription video service, adopted a so-called poison pill to protect against a hostile takeover after billionaire investor Carl Icahn acquired an almost 10 percent stake in the company.

The stockholder rights plan, approved unanimously by Netflix’s board on Nov. 2, would be triggered if an “activist shareholder” acquired 10 percent of the stock, or an institutional investor bought 20 percent, Jonathan Friedland, a company spokesman, said in an interview.

The move is designed to make a hostile takeover too expensive and gives Netflix Chief Executive Officer Reed Hastings a tool to thwart Icahn or other potential buyers. Icahn, 76, said on Oct. 31 he had acquired stock and options representing 5.54 million Netflix shares. He said the video service is an attractive takeover target for larger companies, including Amazon.com and Verizon Communications, that have entered the market Netflix pioneered.