Famed activist investor Carl Icahn recently built a 10% stake in digital video maven Netflix (NASDAQ:NFLX). Icahn noted that the stock seems undervalued, and the company might be ripe for buyout by a larger business. In media interviews, he suggested that Microsoft or Amazon.com might be interested.

Icahn is known for buying large holdings in his target companies, then pushing for a sale or merger of the entire company. Netflix doesn't seem interested in that outcome; this morning, the company created a brand-new "poison pill" for potential acquirers -- like Icahn and friends.

The new stockholder rights plan gives Netflix the right to buy a very large quantity of Netflix shares at a 50% discount if anyone gains 10% ownership of the stock. The limit sits at 20% for certain investors, and Icahn's stake appears to qualify for this limit. The would-be acquirer would see its large ownership disappear in a sea of freshly minted shares.

This poison pill doesn't apply to deals that have been approved by the Netflix board of directors, and it remains in effect until 2015 unless the board buys back the "right certificates" for $0.001 per right. The plan is designed to fend off hostile takeover bids by making it impossibly expensive to buy a controlling stake, but negotiated deals might still work.