In geek speak, there's such a thing as a "good hack." That's when a computer expert pulls off a trick so unusual and ingenious that it astounds his colleagues. The music industry's digital threat to online song swappers last week was a good hack.

Recording industry spies tapped into Kazaa and Grokster, two Internet file-swapping services, and flashed messages to music traders. "COPYRIGHT INFRINGEMENT WARNING," the message read. "When you break the law, you risk legal penalties. There is a simple way to avoid that risk: DON'T STEAL MUSIC."

Analysts say up to 61 million Americans use peer-to-peer services to download copyrighted material. The Recording Industry Association of America is collecting the user names of suspected pirates, but claims it plans no legal action.