A PC that is connected to the Internet via a cable modem (i.e., using a cable television ISP) is always vulnerable to a malicious hack attack whenever the PC is on. Even if a browser is not opened, merely turning on a PC with a cable connection renders the device vulnerable to attack.

Why is this? Because cable ISPs, in providing the Internet access to a user, essentially are creating giant always-connected networks of PCs comprised of all their customers. Cable connections utilize Ethernet cards, which render the user one link in a giant network. Even if a browser is never opened, a cable-connected PC links to the Ethernet-enabled network (i.e., the Internet) as soon as the PC is booted -- just as a connection to a LAN or other corporate network renders the device vulnerable to attacks across that network. This gives a hacker access to the user's hard drive, and opens the door for many kinds of malicious hack attacks.

One way to protect a cable-connected PC from malicious hacks is to disable file-sharing and print-sharing capabilities in the operating system. This is a simple solution for some but for others not a reality as this method basically disables any kind of home networking.

A better method is to install either a hardware or software firewall. A hardware firewall typically is a small device that the cable and the Ethernet card are both connected to. All transmissions pass through the hardware firewall. A software firewall, which is the more common and cheaper of the two methods, is a piece of code that resides on your PC and is always running. The software watches interactions between the PC and the Internet and blocks any suspicious activities.