I can see how a program well short of AGI could "crash" the internet, by using preprogrammed behaviors to take over vulnerable computers, to expand exponentially to fill the space of computers on the internet vulnerable to a given set of exploits, and run Denial of Service attacks on secured critical servers. But I would not even consider that an AI, and it would happen because its programmer pretty much intended for that to happen. It is not an example of an AI getting out of control.