The real kicker is in point 1.13:
> website activity logs show the earliest request on the server for the URL https://obr.uk/docs/dlm_uploads/OBR_Economic_and_fiscal_outl.... This request was unsuccessful, as the document had not been uploaded yet. Between this time and 11:30, a total of 44 unsuccessful requests to this URL were made from seven unique IP addresses.
In other words, someone was guessing the correct staging URL before the OBR had even uploaded the file to the staging area. This suggests that the downloader knew that the OBR was going to make this mistake, and they were polling the server waiting for the file to appear.
The report acknowledges this at 2.11:
> In the course of reviewing last week’s events, it has become clear that the OBR publication process was essentially technically unchanged from EFOs in the recent past. This gives rise to the question as to whether the problem was a pre-existing one that had gone unnoticed.
The report also says a previous report was also accessed 30 mins early.
> In other words, someone was guessing the correct staging URL before the OBR had even uploaded the file to the staging area. This suggests that the downloader knew that the OBR was going to make this mistake, and they were polling the server waiting for the file to appear.
The URLS are predictable. Hedge-funds would want to get the file as soon as it would be available - I imagine someone set up a cron-job to try the URL every few minutes.