One normal way to connect to the Internet from home is through a dial-up connection. The Internet Service Provider (ISP) may then assign you a different IP address each time you connect to the Internet.

The fact that you get a new IP address with each connection may lead you to think that you are safe from attacks. After all, your IP address is not known. Not correct! The fact is that when you are connected, your computer is part of the global network (Internet) and accessible from everywhere. The kind of connection which is possible, and what and outsider is allowed to do on your computer, depends on how your computer is configured.

We have in the security information for week 10 discussed briefly what information you reveal when you are connected to the Internet, as well as a tool which may be used to get such information. Such tools may be used to scan a range of computers (e.g. your ISP's domain), and then try to attack those who seem vulnerable (your computer?).

Another type of attack is explicitly directed at you. Popular IRC (Internet Relay Chat) programs and the very wide-spread ICQ may make your current IP address available to those who see that you are on-line. An intruder may then try to attack your computer. She may look for well known vulnerabilities in the operating system and try to exploit those, or she may exploit vulnerabilities in your chat client/protocol.

Common attacks in such situations are the many Denial of Service (DoS) attacks, which in such a situation are not necessarily dangerous, but which may boot or hang your computer. An irritating situation at the very least.

If an intruder gets access to your computer and are able to log in, she may install Trojan horses (like Back Orifice or Netbus) and take full control over your computer, now or the next time you connect to the Internet.

The moral of this, is that your home computer is not safe from attacks. You should be as security aware when you are connected to the Internet at home as you are at work.

Remove unnecessary protocols. Get to know the vulnerabilities in your systems. Apply the relevant security fixes and patches from the vendors of the programs you use.

Per Olav Førland