Any file sharing program like limewire allows access to your computer. If you don't set it up correctly, you could allow others access to your sensitive files. In a search, I was shocked at the personal files that were available. Some link their upload file location to their "My Documents" folder, which typically is full of your personal and sometimes confidential information. Bottom line - if you don't know what exactly you're doing with those programs - you probably shouldn't do it...

BTW - much worse than that is the amount of viruses that are in the files throughout Limewire world. I'd be far more afraid of that...