This is nonsense. No ISP is "fishing" users on Gnutella. Why do you think the ISP has anything to with that? The IP addresses in results on Gnutella can be trivially forged and
in spam results most of them are really forged. The files are
really trojans or just spam. The hosts that emit these results are either infected hosts or owned by the spammers themselves. As it is so easy to forge IP addresses in Gnutella, filtering IP addresses is not clever at all. It is useless and in the end you will have trouble downloading or finding anything at all because you are filtering everything out. The only IP addresses you might want to filter are those of hosts which really upload these files. However if those are dynamic IP addresses of infected machines, that's useless as well. Filtering only makes some sense for IP ranges that belong to server farms used by spammers.

Assuming that any ISP would try to infect the machines of Gnutella users is very weird though. I really wonder how you get that idea. The infected machines would cause them a lot more trouble than the already have. The legal consequences would be devastating for them. Only business people who consume coke would consider treating their customers this way.