When you are connected to the net your computer is constantly sending out messages (handshakes) to all and sundry (lack of morals you see) to see if they want to talk. Many reply but as you have not given them permission to access they are denied. A firewall sees this as an alert but there is really nothing to worry about as it is only computers 'chatting' each other up.
Also when connected you can be routed through several servers and they will also check to see if your IP is still current so that when you download things they will be sent to the right address. The servers can be anywhere on the planet but as yours was from NTL it would seem that they were just checking if you were open for business
The chances of you getting hacked are virtually zilch; in spite of what is 'reported' about hackers, they are not interested in peoples' utterly dreary computers (like mine) and there are much easier ways of culling bank/credit card details. Turn off the alerts and surf mercilessly.
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