Okay, I'm not savvy on laws. LimeWire, is a software, which is completely legal. It's what's done on Limewire that isn't legal: downloading and sharing copyright material.
LimeWire's defense is that its software is a tool. Like any other tool, its use is dependent on the users. The same hammer that helps build a house can be used to break the back window and rob it. The person who sells the hammer can't be held responsible for how it's used.
In the lawsuit LimeWire was found not guilty, its users are still vulnerable, though. Since September 2003, RIAA has initiated lawsuits against more than 20,000 individuals for alleged illegal file-sharing. The accused individuals receive a letter from the RIAA's lawyers with a settlement offer to avoid going to court. The individuals are identified by their IP addresses. If the individual refuses to pay the settlement -- typically between $3,000 and $11,000 -- the RIAA threatens to sue them by name for a larger amount [source: Wiki].
So, a better question would be: Is Limewire even safe?