Microsoft Corp. on Friday announced it had offered Yahoo Inc. $44.6 billion, making it the company’s boldest challenge yet against Internet giant Google Inc., the Associated Press reports. Under the unsolicited proposal, Yahoo shareholders could receive cash or Microsoft common shares, balancing the total purchase at 50 percent cash and 50 percent stock. The AP notes that Microsoft estimates at least $1 billion in cost savings from the combination and that the company plans to offer significant retention packages to Yahoo engineers, key leaders and other staff. The takeover offer of $31 per share, sent shortly after Yahoo’s CEO resigned, sent Yahoo's share price up 60 percent in premarket trading, while Google fell 8 percent. Demonstrating its tenacity, Microsoft said it will offer a 62 percent premium on Yahoo's closing stock price Thursday, according to the AP. Yahoo, meanwhile, did not immediately respond to requests for comment (Liedtke, AP/Yahoo! News, 2/1/08).