You may recall Comcast getting busted for interfering with peer-to-peer file sharing communications, especially picking on its users who use BitTorrent. Now the Electronic Frontier Foundation (EFF) has released a detailed report (PDF) that comes close to proving that Comcast was "forging traffic." The EFF describes exactly how its experts used Wireshark, open-source packet sniffing software, to show that Comcast was injecting forged RST packets into their communications, effectively telling both ends to hang up.
The EFF asked, "What's so bad about what Comcast's actions?"
One objectionable aspect of Comcast's conduct is that they are spoofing packets—that is, impersonating parties to an exchange of data. Comcast is essentially deploying against their own customers techniques more typically used by malicious hackers (this is doubtless how Comcast would characterize other parties that forged traffic to make it appear that it came from Comcast or its subscribers). In this sense Comcast is behaving worse than if they dropped a propor¬tion of packets under congested circumstances in order to throttle bandwidth usage, or even if they blocked certain ports on their network. In other words, Comcast is essentially behaving like a telephone operator that interrupts a phone conversation, impersonating the voice of one party to tell the other that "this call is over, I'm hanging up."