In the future spamming could sink file sharing, so why not solving the problem now? Spammers use a PHP-like application that renames spam files to match with the words searched. Limewire should be able to automatically generate a random-code search (EG: 02keb4aube3), then block all IP that returned 02keb4aube3 as results. And the whole process could be done in background.
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And, just a trick: to find out the addresses I want to block, I take a Snapshot of my screen in the exact istant the spammer's IP appears.