However, the number of actual music files being traded has stayed high, indicating that the most active downloaders remain online, the research company said.
The drop of 11 percent--from June, when an estimated 6.4 million households downloaded at least one music file, to October, when 5.7 million households downloaded at least one file--seems to show that the entertainment industry's campaign against file swapping is gaining momentum, said NPD Group analyst Russ Crupnick.
"This is the first time that we've seen this kind of significant drop that's definitely not related to seasonality," Crupnick said.
Entertainment companies have closely watched estimates of file-swapping behavior for years, hoping that a combination of lawsuits, education and court battles would ultimately decrease the numbers of people trading music and movies online.
Despite headline-grabbing lawsuits against individuals, the effects on file-swapping behavior.
The months after the Recording Industry Association of America first said it would start suing individuals did see a substantial drop in music downloading through networks such as Kazaa and eDonkey. But the numbers had crept up consistently since then--until the.
Now it appears that many casual swappers have turned to other means of downloading music. The number of music files that are still being traded, however, has remained fairly flat, and actually increased slightly, from an estimated 258 million in June to 266 million in October.
"This is not atypical consumer behavior," Crupnick said. "There will always be some really committed users regardless of whether supply is cut or demand is impacted."