Viruses that knockout internet access?

Anyone know of viruses that might make getting online impossible? I'm working on a friend's PC. He uses dial-up, win98se, doesn't know much about 'puters or security. He has Norton AV, but has never updated it. So, I took it home and threw it on my network (it has a nic which looks to be properly configured and working - it's getting an IP from my router's DHCP server). I can't seem to get online with the thing. So, I updated his AV by downloading the DAT file on my pc, burning it, and putting it on his. Now that I'm running it, it's found 14 viruses so far. I'll see what they are specifically once it's done running, but has anyone seen a virus that will knockout Internet access? Or is it more likely an IE/NIC/win98 issue?

Uggg, ok, some of the viruses include: trojan.bootconf, trojan.slog, deadhat, doomjuice, a whose who of ugly viruses.

OK, removing those did the trick. Sheesh, some semi-nasties there. Used CWShredder, AdAware, HiJack this, NAV, had to boot into DOS to delete a few files...

good times.

Sorry I didn't get to your topic in time to be of some assistance, but.. Yes. Because bugs in the viral code cause all sorts of problems that aren't intended from crashes and dead net connections on - most trojan authors want you to be online so they can gather your information.