More than half a million Sony laptops sold this year contain a software bug that could lead them to overheat, the company said Wednesday.

Sony has recorded 39 cases of overheating among Vaio F and C series laptops that have been on sale since January.

A bug in the heat management system of the BIOS software is to blame. Sony is asking users to either update the software themselves or return their laptops so it can apply the update.

The fault affects 535,000 computers although Sony is asking a total of 646,000 owners to update their machines. The additional 111,000 machines are susceptible to several less serious problems that have also been found in the software, said Sony.

BIOS is present in every PC and runs below the operating system, controlling the most basic functions of the computer and interaction between major components. It's usually invisible to users except for a BIOS start-up message that is typically seen when a PC boots.

The problem affects machines sold both in Japan and the rest of the world.

Japanese models with the problem are the VPCF119FJ/BI, VPCF118FJ/W, VPCF117FJ/W, VPCCW29FJ/W, VPCCW28FJ/P, VPCCW28FJ/R, VPCCW28FJ/W, VPCF11AFJ, VPCF11AGJ, VPCF11AHJ, VPCF11ZHJ, VPCCW2AFJ, and VPCCW2AHJ.

Affected models sold outside Japan are the VPCCW25FG/B, VPCCW25FG/P and VPCCW25FG/W.

Martyn Williams covers Japan and general technology breaking news for The IDG News Service. Follow Martyn on Twitter at @martyn_williams. Martyn's e-mail address is [email protected]