When you download anything from a peer to peer program like Limewire and similar products you are not downloading files from some sort of official database.
You are downloading files from ordinairy PCs like yours and mine (people can get things off YOUR computer as well as you getting things off theirs).
You dont know WHERE the computer is, or who it belongs to it. It may be in Russia, or Turkey, or Brazil, or Australia. It may be owned by a helpful person who wants to spread muascito the world, or it may be owned by a 15 year old kis who thinks its funny to spread viruses to everyone.
Just because a file on their computer is called "Angel" by Robbie Williams, it does not mean it IS. It coudl be a program with a virus in it.
So with any of these types of programs like Limewire you are always taking a risk.