Confirming weekend rumors, Yahoo rejected on Monday Microsoft's $44.6 billion cash-and-stock offer, saying the unsolicited proposal substantially undervalues the company.

In a statement, Yahoo said that its management team, along with financial and legal advisors, believe the offer doesn't reflect cash flow, earnings potential, or recent investments in its advertising platform.

Further, Yahoo said its board would continue to evaluate other "strategic options." 

[ See related Special Report:  Microsoft makes bid for Yahoo | Blog:  Yahoo + Microsoft: What's love got to do with it? ]

"We remain committed to pursuing initiatives that maximize value for all stockholders," the statement said.

Microsoft offered $31 per share on Feb. 1, which was a 62 percent premium over Yahoo's closing price the day before, and was thus characterized at the time as the proverbial "can't refuse" type. However, since then, Yahoo's stock has risen in value and was trading just above $29 on Monday morning.

At the same time, Microsoft's stock has fallen since it made the offer, closing at $28.56 on Friday, down from a close of $32.60 on the day prior to the offer. Microsoft offered to pay $31 for half of Yahoo's outstanding shares and 0.9509 of a Microsoft share for the other half.

Yahoo's executives were rumored to have been searching for a buyer other than Microsoft. However, no buyer has emerged. Yahoo's latest moves mean that Microsoft may have make a more generous offer, or pursue a hostile takeover.

Microsoft said it believes the acquisition of Yahoo would give it the engineering talent and resources to compete better with Google. While Microsoft and Yahoo have had some success with display advertising, Google's has built a fortune on contextual text ads that appear during a search and on third-party Web sites.

With the offer, Microsoft acknowledged it believes that it and Yahoo can't make a credible run at Google unless they fuse into one organization.

However, skeptics doubt that jointly Microsoft and Yahoo will generate the magic potion that allows them to break Google's stranglehold on the search engine advertising market, the largest segment of the online ad market and the source of Google's riches. Far from making progress, Microsoft and Yahoo have seen their share of search engine queries shrink, as people's preference for Google expands.

If Microsoft acquired Yahoo, it would face the perils and traps of integrating its Internet business with Yahoo, which has 14,000 employees and enough internal problems of its own. The integration process could be long and painful, slowing down both companies while Google speeds further ahead. Eliminating redundancies at the staff, technology and product levels would be a major undertaking.

At the product level, Microsoft and Yahoo have many overlaps in areas like Webmail, instant messaging, advertiser services, portals, content sites, mobile services, online media properties and international properties -- most, if not all, based on different technology platforms that would have to be merged. Then there are the long lists of partnerships and customer engagements that they would have to work through and sync up.

Beyond the inherent challenges in fusing its Internet operations with Yahoo, the bid also prompted swift condemnation from privacy advocates in the U.S., like the Center for Digital Democracy (CDD) and the Electronic Privacy Information Center (EPIC). These organizations argue that a combined Microsoft-Yahoo would have too much power over online journalism, entertainment, advertising and other forms of communications, as well as consumers' data.

Microsoft Monday did not immediately issue a reaction to the Yahoo statement. However, it said when making its offer that it is convinced that the time to make a move is now, when it still sees considerable growth for online advertising on the horizon. Microsoft expects the market for online advertising to almost double in size over the next three years, from $40 billion in 2007 to $80 billion by 2010.