Twitter has announced a new shareholder rights plan in a move known as a poison pill, as a way to block Elon Musk's $41 billion buyout offer. The plan, as reported by The Verge, would allow certain shareholders to purchase more stock in response to anyone trying to gain control of the company through the open market.

The move was announced in a Twitter press release, which says the Twitter board adopted the plan in response to "an unsolicited, non-binding proposal to acquire Twitter." Listed in the press release as a limited duration shareholder rights plan, the maneuver is known in the finance world as a poison pill and is rarely implemented, and even more rarely triggered.

The plan will remain in effect for the next year, and will only be triggered if Musk acquires more than a 15% share of ownership in the company. If the plan were triggered, it would require Musk to spend an increasing amount of money to maintain a majority stake in the company--though the billionaire has suggested that he may be willing to throw increasing amounts of cash at the company.