There's something noteworthy about the digital download version of "A Public Affair," the latest single from pop star Jessica Simpson.

No, it's not that the song can be personalized: Simpson and her backup singers actually recorded 500 first names, from Adriana to Zachary, that Yahoo Music will electronically insert at a dramatic moment in the music for $1.99 a pop.

Far more significant is another feature of the song: it is being distributed as a standard MP3 file, with no digital rights management (DRM) technology. And this offering comes from none other than Sony BMG, the record label that has taken the most extreme measures to keep customers from making digital copies of its songs (see "Inside the Spyware Scandal").

Until now, essentially all the legally purchased and downloaded music from the four major record labels, Sony BMG, EMI, Warner, and Universal, has been offered in formats designed to make copying and sharing difficult. Apple's iTunes Music Store -- the source of more than 70 percent of all commercial music downloads -- limits customers to playing its songs on their iPods or up to five "authorized" PCs.

But because it's being released in the most universal audio format, Simpson's song, which debuted on July 19 at Yahoo Music and goes on sale at other digital music retailers this week, can be copied and played on an unlimited number of devices, including the iPod. (Posting such digital files on file-sharing networks for anyone to copy is still illegal.)

Of course it's only one song out of millions available at Yahoo Music, iTunes, and other online music stores. But music-industry watchers are interpreting this promotional offer as an important experiment -- one that may foreshadow a wider loosening of the major labels' restrictive policies.

"This is a sign that the enthusiasm for DRM is beginning to wane in the music industry," says Fred von Lohmann, a senior staff attorney and intellectual-property expert at the Electronic Frontier Foundation (EFF) in San Francisco. "I certainly don't expect DRM to disappear overnight. But I would not be surprised if you saw specific genres or subsidiaries of the major labels experimenting with more unprotected MP3s."