Sony Corp.'s music division said Wednesday it is distributing a free software patch to reveal hidden files that were automatically installed on hard drives when some of its music CDs were played on personal computers.

The offending technology was designed to thwart music piracy but prompted a chorus of criticism.

Sony BMG Music Entertainment and its partner, Britain-based First 4 Internet Ltd., said they decided to offer the patch as a precaution, not because of any security vulnerability as some critics had alleged.

"What we decided to do is take extra precautionary steps to allay any fears," said Mathew Gilliat-Smith, First 4 Internet's CEO. "There should be no concern here."

The controversy started Monday after Windows expert Mark Russinovich posted a Web log report on finding hidden files on his PC after playing a Van Zant CD. He said it disabled his CD drive when he tried to manually remove it.

Russinovich made the discovery while running a program he had written for uncovering file-cloaking "RootKits." In this case, the Sony program hid the anti-piracy software from view. Similar technology has been used by virus and worm writers to conceal their code.

A firestorm quickly erupted over what appeared to be an attempt by the music company to retain control over its intellectual property by secretly installing hidden software on the PCs of unsuspecting customers.

Making matters worse, Sony did not disclose exactly what it was doing in its license agreement, Russinovich said. It only mentions that proprietary software to enable copy protection would be installed. The software affects only PCs running the Windows operating system.

The license "makes no mention that it's going to install something that's going to be hidden from view, that will constantly consume CPU resources even if I'm not listening to music and it will have no uninstall capability," he said.

The copy protection technology, which limits how many times a CD can be copied, was included on about 20 titles, including discs from The Bad Plus and Vivian Green.

Gilliat-Smith and Sony BMG spokesman John McKay said the technology had been on the market for about eight months and there had been no major complaints before Russinovich's blog post. Still, a newer, similar technology was being rolled out before the latest controversy erupted.

The patches that reveal the hidden files are being made available to antivirus companies as well as to customers who visit the Sony BMG site. They do not remove the copy protection software, however.

McKay said customers can download a program to safely uninstall all the software by visiting the Sony BMG Web site at