Attacking network cards

It sounds like this is possible on an already booted machine, remotely, without any software
on the host-machnine? If that's really the case... Let's buy som fast GPIO-interfaces and
bit-bang everything from software within our control :)

On a similar matter, a friend of mines X31 a few years back was set (from factory) by default
to accept remote bios upgrades. That seemed a bit spooky back then, but maybe it's still the
case on business-targeted hardware just to aid easy rollouts in large environments?