Microsoft's $200 million campaign to sell its three-year old Windows XP OS would never have got off the ground without a Mac, it appears.

In an attempt to "showcase" how users can "explore, enhance and pursue their passions" with the OS, Microsoft made one of the new 'Start Something' ads available for download.

Users downloading the ad and using the Get Info command to check the EXIF information about the ad image quickly uncovered Microsoft's Achilles' heel: that information shows the image was made using Adobe CS - on a Mac.

Thanks to Mac Daily News for the tip.