When Tesla Inc (TSLA) CEO Elon Musk on Thursday entered his unsolicited $43 billion bid to acquire and take Twitter Inc (TWTR) private, the company scrambled.

Unpleased with the offer, the board of directors were reportedly debating imposing a method called a “poison pill” to prevent Musk from acquiring the company.

The maneuver, known as the “poison pill” or the “Rights Plan” is a defense tactic used to avoid takeovers by diluting a shareholders stake by creating more outstanding shares in the market.

What Happened: Twitter took the pill.

The company announced Friday afternoon its board of directors unanimously adopted a limited duration shareholder rights plan.

"The Rights Plan is intended to enable all shareholders to realize the full value of their investment in Twitter," the press release states. "The Rights Plan will reduce the likelihood that any entity, person, or group gains control of Twitter through open market accumulation without paying all shareholders an appropriate control premium or without providing the Board sufficient time to make informed judgments and take actions that are in the best interests of shareholders."

What This Means: The rights will become exercisable if an entity, person, or group acquires beneficial ownership of 15% or more of Twitter's outstanding common stock in a transaction not approved by the board.

The measure in place, called a flip-in poison pill, will allow shareholders to purchase additional shares of Twitter at a discount if Musk acquires more than 15% of the company. If shareholders purchase additional shares at a discounted rate, it will further dilute the company’s interest, making the cost of acquisition much higher.

So, if Musk wants to purchase Twitter, it might take more than $43 billion.

TWTR Price Action: Twitter's stock closed Thursday's session at $45.08 per share, down 1.7%.