The year before last I had a hard disk crash on my lap top that necessitated a return to Maxdata for a new HD. When it came back, with XP pre-installed, I needed to download the Avira AV programme so logged onto the internet. Within two minutes malware had got into my system. A bit embarrassing really as I was trying to download one of my securit programmes.
Shouldn't happen to a fully patched up to date system with a stealth mode NAT router between you and the net.
Of course there's a window of opportunity before you download the service packs and patches - which you should of course do
before worrying about any AV stuff - but
still nothing should get past the stealth mode NAT router (or other hardware firewall of your choice).
If you don't have any sort of hardware firewall to hide behind whilst you download the service packs and patches, download them onto another machine and copy them over by USB stick, or take your machine round to your mate's house where there
is a proper router, or do
something -
don't just plug an out-of-date unpatched machine (running
any operating system) unprotected into the net. Even if it has already got AV on it.