there is a guide to unsafe file sizes on the Gnutella network, I can tell you one is 0.0KB, but can't remember any more. It is available as a text file (*.txt) which you can get from any client that uses the Gnutella system. I think it also tells you an incomplete (obviously) list for unsafe IP's, so if you choose Gnutella, search for unsafe, sizes, virus, etc. .txt files can't (well shouldn't, really) harm your computer as they're just .txt's.
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