[Myrddin]

Sniffing is not problem. Actively accessing (transmit/receive) without authorization is intrusion. An unscrupulous techie could easily fix you up with a connection to a private, virus infected web server via your unauthorized connection. Any damage to your computer would be entirely your fault for intruding. Consider carefully what you choose to access.

[rwfromkansas]

They could hack into your closed one as well.

Nevertheless, since I use DSL, they can't use my wireless since I don't have any.