If you are online, you are vulnerable. Yes, cablemodem connections are desirable to a cracker because of the speed of the connection. Netbus, Back Orifice and the like.
Situational awareness is the key here.
You have to see whats going on around you to be able to defend against it. There are a number of log watcher apps out there that will email an alert to you if it sees anything unusual, such as swatch and logcheck. Tools like nessus and nmap are great for this. All I ask is a tall ship and star to steer her by.