An Internet doomsday worm can be created that is so intractable that it cannot be eradicated. The worm would have to operate in the noise level of the Internet. It would have been modular enough to take different payloads. The Pentagon has been plagued by the worm agent.btz; they are still trying to remove it after 3 years. A worm could also have the ability to carry multiple weaponized payloads. Can a worm shut down the Internet? I believe a worm can definitely create access problems. As a political tool it can slow down the internet.
Source: https://thehackernews.com/2011/11/doomsday-worm-sputnik-of-2011.html