An unfixed bug in the USB driver of Windows XP Service Pack 2 can cause a laptop's battery to drain faster when there is a device connected to its USB port, Microsoft confirmed on Friday.

In a public statement, Microsoft also admitted that the flaw, which lies in the ACPI (Advanced Configuration and Power Interface) driver of Windows XP SP 2, will remain without an easy fix indefinitely. The ACPI is part of the operating system's power management scheme for USB 2.0, the latest standard for USB peripheral ports on notebook computers.

The flaw affects some Intel-based laptop computers according to the software maker. The company has been officially aware of this problem since July 2005 when it informed its support and OEM hardware partners of its existence through an article in its knowledge base.

In that article, the company outlined a registry key fix for the bug, but this fix requires a "deep understanding" of the operating system and there are risks involved with implementing it so it is not meant for general customer user, Microsoft warned. Afterwards, a published report discovered the bug in late January, and Microsoft had to publicly acknowledge the flaw.

Microsoft and its third-party support partners are continuing to investigate the bug but do not know if and when they will release a widespread fix. However, the company said concerned customers should contact Microsoft technical support and if demand for a patch is sufficient, it will do additional testing and release a fix on its Microsoft.com/download center.