Ed Felten points to a report (behind a firewall) that the RIAA is making the argument that anti-spoofing technologies on P2P networks may be evidence of inducement under Grokster (RIAA Saber-Rattling against Antispoofing Technologies?). Ed is entirely right that anti-spoofing technologies have both good and bad uses (you want to make sure you get a good connection/copy of that open source program). It is unlikely that these technologies alone will create liability (fact dependent Sony test necessary, however). Nevertheless, I can see under Grokster that if a court does find other evidence of intent that, like using an advertising-based business model or not employing filtering, a court could find the use of anti-spoofing technology to be further evidence of intent. So, if there is no initial evidence of intent, anti-spoofing is probably good. But, if the court finds evidence of intent, then anti-spoofing could be found to be further evidence of bad intent. What a mess.