On Wednesday we discussed the open structure of filesharing and its resulting vulnerability to spam. While there are some similarities between e-mail and gnutella spam, the spoof files have no analogue in e-mail. When MediaDefender puts up spoofs for Rihanna’s Disturbia, unless you are using gnutella to search for Disturbia – which you cannot legally do – the spam has no effect on you. But of course, if MediaDefender is allowed to persist in doing this successfully, gnutella would lose much of its appeal.
The solution that has traditionally been adopted is an IP block list. When MediaDefender puts up spoof files, they come from the IP addresses of MediaDefender’s computers. While it is possible that MediaDefender could (and doubtless would have to) get several computers to perform the spoofing, they are all accessing the internet through a single ISP. Therefore, when an ISP is found to be hosting a spoofing operation such as MediaDefender’s, the entire range of IP addresses owned by the ISP is added to filesharing program’s IP block list. When an IP address is on the block list, other computers will refuse to connect to it, thereby preventing it from filesharing.
Because filesharing becomes useless without something to stop spoof files, IP block lists are a common part of P2P sharing programs. Generally, they are posted on web sites and downloaded by the P2P program, at the direction of the user. The program is generally configurable to download the block list from a site of the user’s choosing, and the block list file is stored in a known location and is readable and editable by interested users. For example, this forum discussion describes how to download the block file for the P2P client eMule.
What is not broadly appreciated is the role that LimeWire the corporation plays in the gnutella network. LimeWire is not merely a provider of software (and there are non-LimeWire gnutella clients, not as popular as LimeWire). Limewire’s client software, aside from supporting the gnutella protocol, receives from LimeWire a cryptographically signed file, called
simpp.xml. This file contains a number of parameters for the operation of the client, including its IP block list. Because of the strong cryptographic signing by LimeWire corporation, no one else may send the list. LimeWire can therefore, at its sole discretion, block hosts from sending data to essentially all of its clients. Anyone putting up files that LimeWire deems unsuitable is knocked off in a matter of hours, and, since LimeWire is by far the most popular gnutella client, the spoofer is effectively shut down.
The LimeWire P2P clients are unusual in that there is nothing configurable about the choice of block list. Moreover, unlike other programs, there is no way for anyone other than LimeWire to send it, and no way for a non-technical user to examine its contents – in fact, the typical non-technical user would not even know that blocking is going on. (The only way to turn off blocking is on an advanced configuration panel.)
(One other interesting feature is also revealed from looking at the
simpp.xml file: LimeWire has added a facility that allows its server, and only its server, to contact a running LimeWire client and ask it various questions about what the client is doing. This feature allows LimeWire to phone up LimeWire clients and inspect them, thereby gathering information about its network. This feature could be used as a sort of mini-spyware, though it is not clear exactly what LimeWire does with it.)
Tomorrow we shall see one way to interpret the legal significance of these behaviors on LimeWire corporation’s part.