Plugging two computers into the same hub is the same as if you try this with
an A to A USB cable. You'll short the two PCs' power supplies together,
possibly destroying one or both machines or causing a fire hazard. Even
there were no danger to the machines from the problem with two power
supplies, there still wouldn't be any way to get the two PCs talking to each
other, since USB doesn't support that particular kind of communication.
'Cross-over' USB cable doesn't have a hub in the middle, this is a bridge.