Virus protection software alone is not enough to combat the threat. Most virus scanners are not designed to block unsolicited inbound traffic from reaching your computer, nor can they make your computer invisible to port scanners. Port scanners, or port probes, are tools hackers use to find vulnerable systems. The port scanner program can scan thousands of IP addresses in a matter of hours and create a list of computers that are ripe for attack. The IP address ranges owned by cable modem and DSL providers are well known in the hacking community.
Many hackers are DSL and cable modem customers themselves.
They know which IP addresses are filled with computers that are always on and unprotected. Thankfully, this is no longer true. It blocks what is known as NetBIOS browsing, but unfortunately using NetBIOS is only one of many ways to gain entrance to your computer. Trojan horses are programs that masquerade as normal programs, but instead contain code designed to break into a system. Remote access Trojan horse programs work like this.