Internet networking suddenly fails on my G4, other devices are fine?

Question

Problem my G4 PowerBook running 10.5.8 has hit this week...
i.e. G4 browsers and program's work fine on my internal network i.e. using Safari to connect to media players and many other bits of internal kit, but any access to the Internet and it's as if I don't have a working connection. This has prevented me connecting to iTunes and all Internet websites, also get connection error while checking for macs os updates. I'm sure I saw an Airport update last week as part of a regular check - so wondering if other networking code changed or mucked up settings like MTU? I get the same issue on WiFi as well as wired LAN. This is the first time EVER I've seen a cable connected Apple or Windows PC come to that fail to connect, so it must be some very base level issue... I guess it could be hardware, if it's the same chip doing WiFi and LAN?
I've tried the tricks some folk have seen work, like boot in safe mode by holding the shift key down during boot and using a fixed IP address rather than DHCP. All other devices, including horrible Windows PC's, work fine accessing the Internet, plus iPhones and iPads... so it seems something has happened to my PowerBook  :-(
Come on Apple, I see several similar issues while wasting a Sunday trying to fix this...
... one problem is even if they do fix it, how do we get it - unless there's a downloadable 10.5.9 how would we get to load it!!
Also, Apple support pages tell me 10.5.8 is the last Leapard update and that I should update my hardware!!!

Answer 1

DNSchanger or Rove viruses
It is a family know as Rove viruses and often called DNSchanger
Infections are caused by user invoked downloads
There is unlikely to be any ongoing risk of further Rove infection
At worst existing infections will inhibit internet access
All known infections reside in /Library/Internet Plug-Ins/
All known infections use cron and not launchd
An infection typically continually assert some of the DNS server addresses below
An infection can login to a local router and change its DNS server addresses
Further details: http://www.dcwg.org
Between  85.255.112.0  and  85.255.127.255
Between    67.210.0.0  and   67.210.15.255
Between  93.188.160.0  and  93.188.167.255
Between    77.67.83.0  and    77.67.83.255
Between  213.109.64.0  and  213.109.79.255
Between   64.28.176.0  and   64.28.191.255