While Google's search share of 60% in the U.S. will certainly be tough for Microsoft and Yahoo to attack, the challenge in many other major countries around the world will be even more daunting: Google's worldwide search share is 67%, according to ComScore."In many top and growing internet countries, including Germany, Canada, Brazil, Turkey and Italy, Google has more than 80% of the search market," says AdAge.

And as if those and other blunt figures don't present enough of a challenge - Microsoft currently has less than 3% search share in the U.K, Germany and Korea - there's also the additional hurdle of European privacy laws and regulations, and the European Union's long-standing contentious relationship with Microsoft. Here's how my colleague Paul McDougall described that privacy hurdle in his excellent analysis of the wide-ranging risks the Microsoft/Yahoo deal faces:

Another area of concern is privacy. By joining forces, Microsoft and Yahoo together will have access to the Web browsing and purchasing histories of millions of Web users-a fact that could draw scrutiny from government watchdogs and consumer advocates. "Microsoft is a lightning rod for attention from governing bodies in both the U.S. and Europe," said Gartner analyst Allen Weiner.

Here's a country-by-country listing showing Google's search share in 10 countries tracked by ComScore:

--Turkey 93% --Brazil 89% --Italy 88% --Canada 82% --Germany 82% --U.K. 79% --France 77% --U.S. 60% --Japan 56% --Korea 12%