Im not trying to acuse you of anything but, it cant happen unless that person has P2P software on their machine and have shared folders or, you really are a hacker and went too far with it. Even if its a new computer she has someone must have installed the P2P app. A machine, whether its old or new, still has to be setup by a user. Said user installs P2P software on their computers and setsup shared folders. So, she is really clueless or just trying to brush you off. Seriously andy, let it go, the more you press the issue, the more she might not like it, dont keep contacting people ok? really, its a waste of time and an invasion of privacy and, in the long run, you would be the one who'd get in trouble, not them. and, they'll lie to you anyway.

The only way to prevent it is to not install P2P spftware and protect your computer with a firewall & an Anti Virus program.

You are only open to the world on a P2P app if its installed on your system without any protection whatsoever, if ports are left open by mistake the worst thing to happen would be aa dos attack. but, that is all up to the user to take steps to protect themselves from hacks, attacks, viruses etc. P2P apps such as Limewire are not responsible for what you do with it.