Your offer just wasn't good enough. At the end of last week, Microsoft gave Yahoo an ultimatum: Agree to a merger within three weeks, or it’s hostile takeover time for you. Yahoo fired back over the weekend, saying Microsoft’s $44.6B offer was still on the low side. While indicating it was still open to discussion, Yahoo seemed to be relying on poison pill provisions to keep shareholders from forcing the company into a deal with Microsoft. Yahoo is also offering special stock option deals to key employees, in hopes of fending off a brain drain at the company. Meanwhile, Google’s share of the search market continues to rise. Of course, Microsoft may be trying to gobble up Yahoo just so it can dominate the instant messaging space, but some observers think there are other reasons. [The image is a cropped version of fighting, bySuperFantastic, made available under a Creative Commons Attribution 2.0 Generic license at flickr.]