nly has to read the trades to see the attacks and open doors being discovered in all the OSs.) Thus, it isn't just enough to run a firewall; the firewall must be run on a locked-down OS. Two general kinds of attacks against systems exist. One is called the denial of service attack. In this case, the hacker sends one or thousands of packets to the server, causing it to spend all its processing power processing these garbage packets so that it has no time left over to do its real job, such as serving up Web pages. The second kind of attack is more invasive. In this case, the attacker tries to gain access to the machine preferably as the supe- ruser. If the attacker achieves this, he or she can do anything that he or she wants. As a superuser, the attacker can set up accounts on the machine for his or herself and his or her friends, read any file, wipe out any file, and SO on. Very clever hackers will therefore edit the log files so that these logs show no trace of the hacker's presence. You can keep log file in a couple of ways. One way is to frequently copy the log file to an obscure directory and change its name SO that its name does not contain "log." The second is to encrypt the file. The latter is only convenient if the firewall application pro- vides this option. The former only works if the log file is copied often enough to capture the hacker's presence before he or she cleans the log file. In general, care must be taken with the use of a packet network and more specifically, the IP protocol on the Internet. In a wireless environment, this is equally critical because the end user is somewhat transparent. The Gateway GPRS Support Node (GGSN) in a GPRS network makes the mobile station's mobility transparent. This just opens the door to more attacks and more complicated solutions. Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. X.25, Inte