Quote from FAA: "Our preliminary work has traced the outage to a damaged database file." UK news source The Independent is reporting that Nav Canada's NOTAM system also suffered an issue.[1] Speculation: corrupting input, either international or North American? E.G. UTF-8, SQL escape, CSV quoting.
edit: Better reporting of Canada's issue from Canada's CBC (and frankly, better reporting about the US, too). [2] "In Canada, pilots were still able to read NOTAMs, but there was an outage that meant new notices couldn't be entered into the system, NAV Canada said on social media." "NAV Canada said it did not believe the outage was related to the one in the U.S., but it said it was investigating."
edit: Better reporting of Canada's issue from Canada's CBC (and frankly, better reporting about the US, too). [2] "In Canada, pilots were still able to read NOTAMs, but there was an outage that meant new notices couldn't be entered into the system, NAV Canada said on social media." "NAV Canada said it did not believe the outage was related to the one in the U.S., but it said it was investigating."
[1] https://www.independent.co.uk/news/world/americas/canada-fli... HN thread https://news.ycombinator.com/item?id=34347520
[2] https://www.cbc.ca/news/us-air-travel-chaos-notam-outage-1.6...