Shell sold 9.5% of its 23.1% stake in Woodside Petroleum in June 2014 and advised that it had reached an agreement for Woodside to buy back 9.5% of its shares at a later stage. Shell became a major shareholder in Woodside after a 2001 takeover attempt was blocked by then federal Treasurer Peter Costello and the corporation has been open about its intention to sell its stake in Woodside as part of its target to shed assets. At a general body meeting, held on 1 August 2014, 72 percent of shareholders voted to approve the buy-back, short of the 75 percent vote that was required for approval. A statement from Shell read: "Royal Dutch Shell acknowledges the outcome of Woodside Petroleum Limited's shareholders' negative vote on the selective buy-back proposal. Shell is reviewing its options in relation to its remaining 13.6 percent holding."

Answer this question, if possible (if impossible, reply "unanswerable"): Shell became a major shareholder in Woodside after a takeover attempt was blocked in what year?
2001