When you use the Internet, be careful, because the Internet can use you. It's a two way street. Information flows in and information flows out. This is a good thing, but it can quickly turn into quite the opposite.

Having your computer connected to the Internet, whether through a dial-up modem or a high-speed connection, has brought us a new type of bad guy - the intruder. These are people who will try to steal information off your computer. Worse, they might even seize control of the computer. (This recently happened to two of my customers. One of them was a doctor’s office. Their Internet provider just terminated their service. My customers were accused of sending malicious emails. As it turned out, they were infected with a virus that took over their computer without their knowledge.)

The bad guys use special programs that scan networks and computers connected to the Internet looking for open ports. These are electronic doorways into your computer.

These scanning programs are not difficult to find. Would you believe that there are places on the Internet where you can download tons of them?

People with always-on broadband Internet connections are on networks. They are especially vulnerable because their Internet address is often fixed. Once they are found by scanning programs, intruders can return to plant Trojan horse programs on their computers.

These are often sent to the victim as an email attachment. The victim is encouraged to open the attachment to get an attractive program. The Trojan horse also is included, although it is hidden from the victim.

The Trojan horse program can use the previously identified open port to send the victim's personal data back to the intruder. Or it can be used to seize control of the computer and use it to attack other machines.

So take some precautions!

Next week I’ll tell you how.