Port scanning

In Linux or Unix get the best portscanner nmap and use it by simply typing "nmap ipaddress", in windows there are many portscanners which are easy to use.

Well, examples on port scanning.. depends what you'd want to do.
If you just want to check on the ports in your own system go to Steve Gibson's website (http://grc.com/ )and do the ShieldsUp port scan.
If not, I can give you some ideas:
1) get yourself port scanning software. You have two choices: download from Internet or write it yourself. One of the many sites for downloadng is http://www.torus.ndirect.co.uk/hacking/port_scan.html, one of the sites with code examples is http://www.kbcafe.com/articles/port.scan.html
2) find yourself a victim or rather find your victim's IP address.(IP address range?)
3) determine which ports you want to scan. Steve Gibson at http://grc.com/ suggests some ports to scan in his SHIELDSUP pages (go there first!)
4)You start your scanner and wait. If all goes well you'll see a list of IP addresses and whether these each of these addresses responds to the ports you selected.

Additional:
- do not try this in a company/university network unless you happen to be CEO, ICT manager or network administrator
- do not try to scan ports that are known to be used by "trojans"
- do not be amazed if the users/owners of any of the addresses react "unfriendly"

As with most software related issues: make very sure that you really know what you want to achieve. A port scan results in (a lot of) data (addresses and open ports with each address). Data is always totally useless if you have no idea what to do with it.

An excellent port scanner is Nmap, written for Unix systems, but ava for NT as Nmapnt which runs from the command line. Examples are included in the documentation. NetCat is another fine product. Also SuperScanner. Keep in mind that it is illegal toscan someone else's network.

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