Hewlett-Packard ($8 billion) and Nike ($5 billion) also unveil major stock repurchase programs. Microsoft CorpÔÇÖs plan to buy back its shares from investors, which will run until 2013, is said to be the biggest single buy-back plan in history. Analysts say the move is an attempt by the company to use its spare cash to prop up its share price, which has fallen nearly 30 percent this year, partly due to its failed $47.5 billion bid to acquire Internet portal Yahoo.