The overheating is caused by a bug in the bios (basic input output system) software which provides the basic functionality for the machine, rather than the Windows operating system which runs on top of it. The bios is embedded in the chips of the machine, but can be upgraded. Sony says that people should either apply the update themselves, or take the affected machines to a Sony repair centre.
Affected models sold outside Japan are the VPCCW25FG/B, VPCCW25FG/P and VPCCW25FG/W.
Approximately three quarters of a million machines are thought to be affected.
The BBC reports that, though no one has been harmed, the flaw can damage machines:
Although there are no reports of any users suffering burns, Sony say it has received a number of reports of its laptop overheating, distorting keyboards and casings.
Here’s a link to the fix on Sony’s European website taken from the news story.
(I tried to get a link to a North American page, but the flash on Sony’s front page didn’t work in any of my browsers. In Opera, it winked at me, but none of the links worked. In Firefox and Konqueror, the flash was completely non-responsive. In Epiphany, all I got was an empty hole in my screen. Anyone who has better luck is welcome to post a link in the comments.)