Is it possible to crash or shutdown the entire Internet?

Well with skynet it is possible. But realistically, it is impossible you might disconnect connection from country to country but within that country it is impossible. The use of satellites for data transter/signals also made it impossible to stop the internet. But a big solar flare is the most possible scenario.

Nice topic for your first post. Welcome to mylot. As no one knows how the Internet really works, or even how big it is, it must theoretically be possible to shut it down. However, the likelihood of that happening must be extremely small. Not that people aren't trying! There are a lot of sick people out there. Virus, trojans and worms may effect thousands of computers but the Internet is really just a collection of wires, satellite links, and routing hardware. More worrying to me is the idea that, if the Internet is gone, then mankind will be gone too. Afterall, it could always be nuked!