The answer is at click here
I have to say, this sounds like one of the dafter 'anti-hacker' approaches I have heard of - what is wrong with just blocking ports?
What if you are in the middle of a download / email transfer / page update, when your IP address changes?
What if it changes to an address that a 'hacker' is actively scanning? What if it changes to one outside of your ISP's allowed range? I could go on.....