Guess what this is? 

 

It's your IP address, and with this innocuous little number people can find out lots about you. Try it yourself by clicking this link What are my details?
For instance what town/city and country that you live in, who your internet service provider is and therefore probably your telephone company. With a little more investigation whether or not you have a fire wall, whether it is a real one or the one that XP includes for free. They can tell what browser you are using and even how many colours your video graphics card is set at.
They can tell what ports are open on your pc by software like MSN Messenger ( click here for reasons why you shouldn't leave this on when you are not using it ) creating a tunnel into your most sensitive information.

 

 

 

 

 

 

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