It's your firewall or system's natural response to any program downloaded from the internet.

As far as Gnutella network viruses go, see WARNING: Viruses on network you should be aware of! (click on blue link)

For firewall access see: Windows Firewall - LimeWire or User Cant Connect - LimeWire

Other good links to see are the Stickys at the top of this section: Getting Started Using LimeWire - Gnutella Forums & also see How to find music