Reacting to criticism of its CD copy protection, Sony on Wednesday posted a patch that reveals files previously hidden by a rootkit. But that may be closing the barn door after the horses bolted, since hackers are already discussing ways to use the rootkit to conceal their own code.

Wednesday, Sony put a patch on its Web site that "removes the cloaking technology component on SONY BMG content protected CDs," according to a statement on the site. The patch can be downloaded and installed while online, or a 3.6MB file can be retrieved for later installation.

But even as it posted the patch, Sony defended the technology. "This [rootkit] component is not malicious and does not compromise security. However, to alleviate any concerns that users may have about the program posing potential security vulnerabilities, this update has been released."

Although Sony said it has been using the First4Internet-developed digital rights management (DRM) software on selected CDs for several months, it was only this week that researchers discovered the technology relied on a rootkit to hide files. The practice was quickly condemned by other security experts because rootkits are typically only used by virus, worm, and spyware writers to hide their code.