Sometime in the last two weeks my father had overnight been unable to access MSN, Hotmail and Windows Updates. The problem also extended to him not being able to connect to me using the NTR remote connection software that we use, however he did still have VNC installed.

Once he connected to me via reverse VNC and I'd confirmed that he had made no changes to system, been hijjacked or infected. We left it overnight to see if it was a transient problem.

It wasn't.  He is with AOL broadband and apparently they have have made some changes. 

The MTU settings in the Netgear router they supplied are the source of the problem. 

This is how to fix it:

1. Locate the control panel for your Netgear router, standard address ** is http://192.168.0.1
2. Open a web browser and log in to the control panel, standard username and password are admin and password
3. Scroll down the left hand side and find the menu option called Advanced Setup and then click on WAN Setup
4. Scroll down that page and find the option MTU and change the value in the box to 1400 (it was set to 1458)
5. Apply the settings - this also reboots the router - and you're all done.

** if it is not at the standard address you can find it out by determining your default gateway.

On a Windows machine:

1. Go to Start, then Run (or use the search box in Vista) and type in cmd then press enter.
2. In the black window that pops up type in ipconfigand press enter.
3. In the results that follow the Default Gateway is clearly listed, make a note of this and return to the steps above.

On a Apple machine see this article: How to find your router on an Apple Mac