Last week, we reported on mounting evidence that Comcast is targeting and disrupting BitTorrent traffic on its network. Further digging by interested parties has turned up more indication that BitTorrent isn't the only popular P2P protocol being tampered with by the United States' largest ISP.

The Electronic Frontier Foundation noticed the same sort of packet forging that the AP did (and that Broadband Reports readers did some time ago), and continued its testing to see if other applications are affected. The answer is a disturbing "yes." The results of additional testing done by the EFF indicate Comcast is sending forged reset packets with some Gnutella traffic. When the EFF ran a Gnutella node on a Comcast connection, the forged reset packets disrupted communication between the nodes.

What's particularly insidious about Comcast's packet forging is that it's transparent to both its customers and those on the opposite ends of the connection. Applications such as BitTorrent and Gnutella retain some of their functionality, but they'll also appear to malfunction for no apparent reason.

Even if you accept the argument that all P2P traffic is inherently evil, and that Comcast has the right to disrupt it in order to put a stop to copyright infringement, Comcast's traffic-shaping efforts have apparently extended beyond the realm of P2P and into good old enterprise groupware. Kevin Kanarski, who works as a Lotus Notes messaging engineer, noticed some strange behavior with Lotus Notes when hooked up to a Comcast connection last month.

When Lotus Notes users attempt to send e-mail with larger attachments over Comcast's network, Notes will drop its connection. Instead of a successfully sent e-mail, they're greeted with the error message, "Remote system no longer responding." Kanarski did some digging and has managed to verify that Comcast's reset packets are the culprit. Instead of passing the legitimate e-mail through its network, Comcast's traffic monitoring tool (likely Sandvine) is sitting in the middle, imitating both ends of the connection, and sending reset packets to both client and server.

So far, Comcast has been extremely tight-lipped about what's going on here. The only thing Comcast will admit to is using "the latest technologies to manage our network to provide a quality experience for all Comcast subscribers." From the look of things, that quality experience doesn't extend to BitTorrent, Gnutella, and Lotus Notes—and we wouldn't be surprised to see more applications added to that list.

Whatever its methods and motivations are, Comcast's actions are giving advocates of network neutrality legislation new ammunition. Gigi B. Sohn, president of Public Knowledge, said that Comcast's actions demonstrate the need for legislation. "Add this incident to the Verizon behavior on text messaging and AT&T's censoring of the Pearl Jam concert and it's clear that the policymakers who kept saying, 'Wait until there's a problem' before acting on legislation to keep the Internet free and non-discriminatory have to wait no longer," said Sohn in a statement. "We have a problem, and it's time to act on it."

We've requested comment from Comcast on these latest developments and will update this post as they become available.