Following on from http://mgmcc.forumotion.net/internet-f6/internet-access-t224.htm
I got to a stage where I still got logged out from the Internet about every 3 to 4 days.
Virgin TS diagnosed this as an "authentication failure". and the last guy suggested that I ticked the box
"Respond to Ping on Internet WAN port" under "WAN Setup" on my Netgear DG834G router.

The Help file relating to this states:
Respond To Ping On Internet Port

If you want the DG834 to respond to a 'Ping' from the Internet, click this check box. This can be used as a diagnostic tool. This can be a security problem. You shouldn't check this box unless you have a specific reason to do so.

A post on the CA forum got me worried:
"....done a bit of research am now a little concerned about the security of this setting.
I went to this site https://www.grc.com and ran the shields up test before and after. the before was showing as secure and in true stealth but the true stealth analysis failed when "respond to ping on internet wan port" was enabled...."

Should I be concerned? - It does seemed to have done the trick

Thanks - Dave

No, you don't need to be unduly concerned. It is less of a security risk when it is a Router which has your public IP address and responds to 'pings' than if the PC was connected directly via a dialup or USB ADSL modem.

Internet "nasties" looking for unprotected computers to infect will send out pings to establish which IP addresses respond, so they can then infect the computers at that address. They cannot infect your router, although all PCs connected to it should obviously be fully protected with up-to-date AntiVirus and Anti-spyware software.

Also, I recall a posting from "kitz" some time ago in which she mentioned things (don't remember what) that wouldn't function properly if responding to a 'ping' was disabled.

Thanks Mike