Just yesterday, activist investor Carl Icahn revealed that he has invested another $500 million into AAPL stock. Just around 24 hours later, Icahn has posted on Twitter that he invested another $500 million. That brings his total investment into Apple stock to $3.6 billion. This means that he is closing in at 1% ownership of Apple’s stock…

Bought another $500mil of $AAPL tday, bringing our total to $3.6 billion. If board doesn’t see AAPL’s ‘no brainer’ value we sure do.

— Carl Icahn (@Carl_C_Icahn) January 23, 2014

Alongside that announcement, Carl Icahn has taken another shot at Apple’s Board of Directors, saying that the Board does not see the value of Apple’s stock as a “no-brainer.” Yesterday, Icahn also said that Apple is doing a “disservice” to its shareholders in terms of its current, limited share buyback programs.

Carl Icahn has been regularly speaking to Apple CEO Tim Cook and CFO Peter Oppenheimer. He has been urging the pair along with Apple’s Board of Directors to instate a $150 share buyback program. Icahn has worked with Apple to put the proposal up to a vote with Apple’s shareholders. Apple’s shareholders will have the opportunity to vote on the proposal. Apple, for its part, has asked shareholders to vote against Icahn’s proposal:

Icahn has also just published his promised letter to Apple shareholders. Here it is, in full:

The Board recommends a vote AGAINST Proposal No. 10.

The Board and management team are thoughtfully considering options for returning additional cash to shareholders and are currently seeking input from shareholders as part of the Company’s regular review.

The Company’s success stems from the Company’s unique ability to combine world-class skills in hardware, software and services to deliver innovative products that create new markets and delight hundreds of millions of customers. This success has created tremendous value for the Company’s shareholders.

$AAPL is currently up today following these announcements from Icahn: