Worldwide financial markets would certainly be among the first sectors to be fried by an Internet apocalypse, but a Wall Street doomsday scenario doesn't require a full-on Internet crash. In 2014, a wave of reports percolated into the mainstream media regarding the sophisticated and apparently relentless cyber attacks that Wall Street banks fend off every day.
The 2014 attacks reportedly led to the theft of multiple gigabytes of sensitive data, prompting the FBI and the Secret Service to team up with Wall Street's own massive IT security apparatus. It's big business, all right: JP Morgan, one of the banks said to have been targeted by the hackers, has an annual IT security budget of $250 million, with 1,000 dedicated staffers.
If world financial markets were to be significantly disrupted by way of coordinated cyber attacks, the effects would be colossal -- an economic end-of-the-world scenario. (Hollywood, by the way, has been scaring us with this scenario for a surprisingly long time -- if you can believe it, the cult classic "Hackers" is now 20 years old.)