Older versions of the popular music-sharing program Napster were rendered obsolete late last week by the launch of a new program that would help the company comply with court rulings ordering it to stop copyrighted music from being traded online.

Napster began using filters in March to block copyrighted material after it became evident the company might lose a lengthy court battle with the recording industry.

However, the old filter was easily defeated by misspellings of the artist or song title, allowing an underground network of “Napster code” to develop, where users would drop vowels to add letters to confuse the filter.

Using a new file-identification technique called “acoustic-fingerprinting,” the new program will hopefully prevent users from trading any copyrighted material, whether the song is spelled correctly or not, Napster says.

—Shelley O. Abadi contributed to the reporting of this story