Could this possibly have something to do with the limit of 10 TCP connections per machine for windows XP? Its some sort of security feature, the idea being that the computer can only have a connection 10 other computers at any one time, thus if it is infected it can only infect another 10 computers. They failed to realize that those 10 can then infect another 10 and so on... so it really doesnt do anything except delay the infection about 2 seconds.
Try googling "windows xp 10 connection TCP limit" and see what happens.
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