The RIAA started the practice yesterday, said the paper, alerting users of Kazaa or Grokster with the messages DON'T STEAL MUSIC and other notices warning people risk legal action.
The RIAA is likely to distribute as many as a million such messages every week, according to the newspaper.
Grokster and Kazaa cannot stop the RIAA from issuing the messages using the IM system.
Last week the RIAA suffered a setback in its campaign to prevent file sharing networks when a Californian judge said that Grokster and Streamcast hadn't breached copyright legislation.
That's a ruling the RIAA will appeal against. µ