Wireless tapping.

Piggybacking, which is the usually unauthorized tapping into someone else's wireless Internet connection, is no longer limited to hackers. Ordinarily upstanding people are tapping in, and many say it doesn't feet Like theft because it doesn't seem to take anything away from anyone. Piggybacking is increasingly an issue for people who tire in densely populated areas, or for those in buildings where Wi-Fi radio waves easily bleed through watts, floors, and ceilings. "The best case is that you end up giving a neighbor a free ride," says David Cote of Symantec Security Response, which makes computer-security software. "The worst case is that someone can destroy your computer, take your rites, and do some realty nefarious things with your network that get you dragged into court." Most wireless routers come with encryption software for securing the network, but many people don't bother to install it.