Twitter's board of directors voted unanimously Friday to adopt a limited duration shareholder rights plan, or "poison pill," that would immediately dilute the shares of any shareholder who bought 15% or more of existing shares — likely thwarting, for now, a takeover bid by Elon Musk.

"Poison pill" strategies date back to the 1980s, when hostile takeovers started to become more common in the corporate world. In the case of Twitter, the shareholder rights plan that was just adopted will remain in effect for one year, until April 14, 2023.

"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," the company said in a press release.

Musk hasn't yet given up his battle to wrest control of Twitter for himself — something he previously did at Tesla before the company went public, pushing out its founders in 2007/8. But when he made his "best and final offer" on Wednesday to buy up all existing Twitter shares at $54.20 apiece, he said he would "reconsider [his] position as a shareholder" if the offer was rejected. As the New York Times notes, Musk spoke during a TED event Thursday and said never likes to lose, and he proceeded to post another in a series of Twitter polls — asking whether his $54.20-per-share offer should be put to a shareholder vote, and of course 83.5% of his followers voted "Yes."

Musk said Thursday he was "not sure" if he'd succeed in buying Twitter and taking it private, but he hinted at some Plan B, of which we still don't know the outlines.

Musk may just be up to one of his usual, very public games, toying with his nemesis the SEC while he potentially manipulates Twitter's stock price. But he says that he sees the intrinsic value in Twitter and wants to reshape it for the future in his more libertarian image.

Calling Twitter the world's "de facto town square," Musk said Thursday, “it’s really important that people have the reality and the perception that they are able to speak freely within the bounds of the law."

"My strong intuitive sense is that having a public platform that is maximally trusted and broadly inclusive is extremely important to the future of civilization," Musk added.

Interestingly, since Musk upped his stake to own 9.2% of Twitter stock as of last week, another large shareholder, Vanguard Group, has upped its stake and now owns 10.3% of Twitter — becoming the largest shareholder and setting themselves up to rival Musk for control.

There's also the potential for Elliott Management Corp., which owns 4% of Twitter, and whose CEO actively sought to oust Jack Dorsey as CEO (and succeeded), to launch their own takeover bid or something else.

The new "poison pill" plan, though, thwarts any of these efforts at least for the next year.

Twitter's new CEO, Parag Agrawal, held an all-hands meeting with Twitter employees Thursday to reassure them about the whole situation. Agrawal's comments were entirely reassuring though. "This provides all of us with this moment where we feel distracted, where we feel a loss of control,” Agrawal reportedly told employees, per the Times. “I am personally going to spend my time focusing on things I can control, and I believe it will matter."

Those don't sound like the words of a man who knows how things are going to shake out.

Previously: Yep, Elon Musk Is Officially Trying to Buy Twitter in a Hostile Takeover Bid

Photo: Chris J. Davis