These CD's, all bearing "Content Protected" labels on the packaging (meaning "copy protected"), do something very sneaky if you try to play them on a Windows PC: they install a proprietary watchdog program that prevents you from copying the CD more than twice. (On a Macintosh or Linux machine, these CD's play just fine, without any copy protection.)

Last week, a programmer and blogger named Mark Russinovich dug a little deeper, and found out something disturbing: the Sony watchdog program not only installs itself deep in the core of Windows-it's what's called a rootkit-but it also makes itself invisible.

The record company doesn't dispute Russinovich's findings. "The cloaking is an additional level of protection to hide the protection files themselves," Mathew Gilliat-Smith, CEO of First 4 Internet, told me. "It's an extra speedbump to make it that much more difficult [for prospective music pirates] to circumvent the protection." But Sony BMG didn't seem to be prepared for the outcry from privacy advocates and ordinary citizens who felt violated.

To them, Sony BMG's tactic was dangerous, sneaky, intrusive and maybe even illegal. Some of the problems:

* The hidden-rootkit trick has been used by virus writers to conceal their tracks. It doesn't give you such a rosy feeling to know that Sony BMG is treating you the same way.

* Once hidden, the copy-protection software is invisible to antivirus programs, too. So the baddies of the Internet could, in theory, use Sony's software as a backdoor to infect your machine, and your virus checker would miss it.

* If you try to remove the software manually, you risk disabling your CD player completely. (Instead you should use the Uninstall link on Sony BMG's customer-service Web site, whose link appears on the Help screens of Windows Media Player. Of course, then you can't play the CD on your computer.)

* When you insert one of these music discs into your PC, one of those software license agreements appears. It says explicitly what's about to occur: "This CD will automatically install a small proprietary software onto your computer. The software is intended to protect the audio files on this CD. It will reside on your computer until it is removed or deleted."

But this note does not say that the software hides itself. And, even more damning, you don't see this note until you've scrolled down to the third page of legalese in the license agreement. Let's not kid ourselves: NOBODY ever reads those license agreements. They're too long, too opaquely written and generally of little use to anyone except the lawyers.

* Sony's copy-protection software prevents you from playing the music you've bought on your iPod, which happens to be the world's most popular music player.

Once the true nature of the Sony BMG software tactic became public, the company wasted no time in attempting to defuse the issue. Within 48 hours, it released a patch that makes its software visible again; you can download it from http://cp.sonybmg.com/xcp. (Click the Software Updates button.) Sony also provided the rootkit-cloaking information to antivirus-software companies, so that the software will no longer be a potential virus magnet.

At that same Web site, you'll find, incredibly, a link to a Sony-sanctioned workaround that lets you copy the protected songs to the iPod. (Sony says it will send you the workaround by e-mail once you supply the name of the CD and other information.)

Finally, Sony has abandoned the rootkit protection method. (It says, in fact, that it had planned to do so even before the trick became public.) It still intends to install copy-protection software on every audio CD-but it will use other methods.

For now, then, it seems that the cloaked-rootkit issue is dead. If you bought one of the 20 affected CD's, you can uncloak the software, and Sony won't be using this scheme anymore.

My take? Audio CD's that install software onto your PC are just creepy. I believe that distributing copies of a CD to the Internet at large is wrong, so I understand the record companies' concern. But installing secret, self-masking code onto customers' computers seems just as wrong.

It's an "any means necessary" approach to the problem, like dealing drugs to raise money for charity.

Personally, I can't understand why any music fan would buy one of these discs. If you really want a song from Sony BMG, why not just buy it from one of the online music stores and avoid the whole issue? Sony BMG would soon get the message that customers don't like being treated like criminals.

I was also surprised at how dismissive Sony BMG and First 4 Internet seem to be. "It's a tempest in a teapot," Mr. Gilliat-Smith says. "It's benign content protection. It's not malware, it's not spyware-it's innocent.

Consumers, for eight months, have been using these discs with positive feedback. When the issue arose, we addressed it very quickly."

I wondered if he could even understand why consumers might feel a bit violated. I pointed out that the usual damage-control plan for public-relations disasters (see also Tylenol; Perrier; Pentium bug) is not to haughtily dismiss customer fears, but to apologize profusely.

But the closest thing Mr. Gilliat-Smith would say is, "We understand what the concern was, but there was no intent. We reacted as quickly as we could, took responsive issues. And now, hopefully, we move on."

Visit David Pogue on the Web at DavidPogue.com