Speculation that Yahoo Inc.’s once-spurned suitor, Microsoft Corp. , is preparing another takeover bid drove up shares of the struggling Internet search company. Yahoo’s shares saw their biggest weekly increase since November 2008. Reuters reported that Microsoft is considering whether to make an offer, and that fed the takeover speculation that has swirled around Yahoo since it fired CEO Carol Bartz five weeks ago. A Microsoft spokesman declined to comment. Microsoft is viewed among investors as the most tantalizing candidate to buy Yahoo because the software maker has the cash to pull it off and a history with its rival that makes a takeover seem like a realistic scenario.