[ Thanks to Rich
Jankowski for this link. ]
“Recently the media has been covering many Internet
break-ins, their reporters spinning tales of clever bandits who
magically gain access to machines with a simple keystroke. In real
life, however, it is rarely that simple. Cracking into a
computer system requires planning. A cracker has to find a target
machine, and then find out what ports the machine is listening on
before a system can be compromised.”
“This is usually done through scanning, the art of finding
machines on a network and testing them to see what ports are
listening. Scanning networks and hosts is the first strategy a
cracker will use before launching an attack. By using scanners such
as Nmap, the “bad guys” are able to sweep networks and look for
vulnerable targets. Once these targets are identified, an intruder
is able to scan for listening ports. Nmap will also use TCP stack
fingerprinting to accurately determine the type of machine being
scanned.”
“This article will cover the use of Nmap to allow a security
administrator to probe his/her site to get a “cracker’s view” of
his/her network. By employing the same tools used by an intruder,
an administrator will see what his/her site looks like to the bad
guys, and hopefully will be able to initiate steps to help secure
his/her systems.”