By Edwin Chan and Sam Forgione SAN FRANCISCO (Reuters) – Activist investor Carl Icahn lashed out against Apple Inc again on Wednesday, and tweeted that he had bought $500 million more shares in the company in just the past two weeks, bringing his investment in the iPhone maker to over $3 billion. The billionaire, who has repeatedly urged Apple to return more cash to shareholders, told CNBC later in an interview he intends to buy more stock at some point in one of the greatest no-brainers of all time. Icahn, known for decades of strong-arm tactics including proxy fights against major corporations, said on Twitter that the company was doing shareholders a great disservice by failing to boost its share buyback program. Icahn has repeatedly made it clear that he does not oppose Apples management.