Editors' note : We have received word from SonyBMG that the DRM is not implemented in CDs produced from this region. Copy-protected discs will have stickers pasted on the cover to reflect that fact. Though the content protection software can be uninstalled with a call to Sony's customer service, the consumer must be aware that by doing so, the CD will not be playable on the PC until the application is reinstalled.

Mark Russinovich was doing a routine test this week of computer security software he'd co-written, when he made a surprising discovery: Something new was hiding itself deep inside his PC's guts.

It took some time for Russinovich, an experienced programmer who has written a book on the Windows operating system for Microsoft, to track down exactly what was happening, but he ultimately traced it to code left behind by a recent CD he'd bought and played on his computer.

	Two for the price of one--Buy music, get rootkit.

The SonyBMG-produced Van Zant album had been advertised as copy-protected when he'd bought it on Amazon.com, and he'd clicked through an installation agreement when he put the disc in his computer. What he later found is that the software had used a sophisticated cloaking technique that involves a "rootkit"--something not dangerous in itself, but a tool often used by virus writers to hide all traces of their work on a computer.

"We're still trying to find a line between fair use and digital rights management, and it is going to take issues like this, with discussions between lawmakers and industry, to come up with what's fair and honest," Russinovich said. "But I think this has gone too far."

Russinovich posted a detailed step-by-step account of his findings on his blog, drawing immediate criticism of SonyBMG's technology from some inside the security software community. The passionate response underlines the power copy protection retains to inflame emotions and spark bitter debate, despite the growing string of chart-topping albums that have been released over the past year with the protections included.

A handful of security companies weighed in on the issue, saying the rootkit could present a possible--if still theoretical--risk to computers.

The creator of the copy-protection software, a British company called First 4 Internet, said the cloaking mechanism was not a risk, and that its team worked closely with big antivirus companies such as Symantec to ensure that was the case. The cloaking function was aimed at making it difficult, though not impossible, to hack the content protection in ways that have been simple in similar products, the company said.

In any case, First 4 has moved away from the techniques used on the Van Zant album to new ways of cloaking files on a hard drive, said Mathew Gilliat-Smith, the company's CEO.

"I think this is slightly old news," Gilliat-Smith said. "For the eight months that these CDs have been out, we haven't had any comments about malware (malicious software) at all."

A SonyBMG representative said the software could be easily uninstalled, by contacting the company's customer support service for instructions. Those instructions are not specifically available on the Web site that answers questions about the company's copy protection tools.

Root kit realities
Root kit software has been around for over a decade but has recently come to increased prominence as more writers of viruses and the like adopt it for their purposes. Essentially, rootkits are tools for digging deep into a computer's operating system to hide the fact that certain software files exist or that the computer is performing certain functions.

Unlike other, less-powerful means of hiding files on a hard drive, rootkits are created to be extraordinarily difficult to uninstall without specific instructions, rooting themselves in an operating systems' deepest recesses in order to prevent their deletion.

In the case of the SonyBMG software, trying to remove it manually could shut off access to the computer's CD player, researchers said.

BMG--Buy My Goods, or else...

Security researchers note that simply hiding something doesn't make it a threat, and the SonyBMG software is designed to hide the digital rights management tools that prevent unauthorized copies of the CD from being made.

However, it does remain active in the background of a computer, taking up a small amount of memory, even when the CD is not being played. Thus the rootkit software does have the potential to be misused by others, according to some researchers. The First 4 Internet software's technique for hiding files is broad enough that it could be adopted by virus writers, allowing them to hide their own tools on computers that have run the software from the CD, say some security experts.

That's an "academic" concern, but a real one, said F-Secure chief research officer Mikko Hypponen, who wrote a warning on the issue Tuesday.

"Right now if you have this on your system, there is no real-world risk just because of this," Hypponen said. "But it would not be too far-fetched that some virus writer would try to take advantage of this."

Giliat-Smith said his company is working with major antivirus software companies to help their software recognize the copy-protection tools and help guard against misuse.

What is Sony going to do?