since many cable internet users share the same media for sending and receiving data, is there a way to listen?

i know that the backbone of cable networks cary alot of user information through the network. In that case, could anyone , perhaps a hacker listen in on that line an collect user information?

The data is encrypted to prevent one from eavesdropping on their neighbours traffic, but it doesn't prevent one from observing it's existence. Prior to DOCSIS 3.0 published in 2006 the encryption is the rather weak DES, which can broken in about one day with a $10000 (2006 prices, cheaper today) machine.