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Comcast's interference, on the other hand, appears to be an aggressive way of managing its network to keep file-sharing traffic from swallowing too much bandwidth and affecting the Internet speeds of other subscribers.

Comcast, the nation's largest cable TV operator and No. 2 Internet provider, would not specifically address the practice, but spokesman Charlie Douglas confirmed that it uses sophisticated methods to keep Net connections running smoothly.

Further analysis of the transfer attempt from the Comcast-connected computer in the San Francisco area revealed that the failure was due to ''reset'' packets that the two computers received, carrying the return address of the other computer.

Those packets tell the receiving computer to stop communicating with the sender. However, the traffic analyzer software running on each computer showed that neither computer actually sent the packets. That means they originated somewhere in between, with faked return addresses.

The short answer: Badly. Based on the research, conducted by Terry Shaw,
of CableLabs, and Jim Martin, a computer science professor at Clemson
University, it only takes about 10 BitTorrent users bartering files on a
node (of around 500) to double the delays experienced by everybody else.
Especially if everybody else is using "normal priority" services, like
e-mail or Web surfing, which is what tech people tend to call
"best-effort" traffic.