[ConcernedCitizen]

With regard to Internet attacks and cost of damage due to downtime or otherwise, I clearly remember Mafia Boy back In 2000.

at 15 years old, he executed a massive denial-of-service (DoS) attack that crippled some of the internet’s most popular websites. Calling the attack Rivolta, meaning “riot” in Italian, he brought down Yahoo!, eBay, CNN, Amazon, and other sites, causing an estimated $1.7 billion in damages.

It was, for Its time, a very significant and costly attack.

This is indeed very significant loss of connectivity. Yahoo, at its peak, serviced about a billion users with email and games. That's a conservative guess. It was a loss of both communication and ad revenue for the company.