What is Satan attack and IP spoofing ?

What is a Satan attack and IP spoofing?
And how could I programmatically defend the system from these?
I mean "How could I write a program defending from such kind of problems"?

I would appreciate any help.

Thanks !

Satan is a tool designed to probe a computer system for security loopholes, (Security Administrator Tool for Analyzing Networks). See, for example, http://www.cs.purdue.edu/coast/satan.html
Use of Satan is not inherently bad. Network coordinators sometimes run it against their own machines to probe for weaknesses which they can then fix. Running it against a machine you don't own is regarded as a hostile act (and may be illegal under some jurisdictions).

IP spoofing is a mode of attack in which one machine generates internet traffic purporting to be from a different machine, in order to gain access with that machine's attributes. see, for example,
http://www.hotwired.com/i-agent/95/15/bellovin.html

You would normally defend yourself by running Satan yourself and fixing anything it reports, and by using a more secure authentication method rather than writing a program.

The first link above gives information on hallmarks of an attack, which your program could watch for. The original Satan was aimed at UNIX boxes, so I would suspect that some of the things that it exploits are not normally a problem on platforms where you can use VC++.