Adam Sitzes’s dossier included details of the RAF’s £125m Typhoon jets, and named US counter-terror staff based here.
He transferred it unencrypted, put it on public view then is feared to have forgotten it — gift-wrapping it for China or Russia.
Arms deals were exposed, and emails unmasked National Security Agency staff in the US, plus top officials in the UK, Nato and Ukraine.
A source said: “These type of errors end careers.”
US Air Force worker Sitzes, in his 40s, uploaded thousands of pages to file-sharing website Trello in 2020.
Crucially he gave them public access so he could view them on any device and work from home.
The Sun was alerted to the data’s presence online and found it in seconds from a Google search.
We alerted Whitehall, they told the US who scrambled to remove all files. Ex-CIA terror expert Aki Peritz said: “Making sensitive information available in one place, on a specific topic, with a shiny red bow tying it all together makes it easy for an adversary to exploit.
"It’s so stupid.”
Sitzes’ social media have been deleted.
A source added: “He’s likely to face an immediate investigation.”