Dave Verwer, writing for iOS Dev Weekly:

From what I can determine from the tweets, there was about a 30-45 minute period when people logging in to iTunes Connect were seeing other random accounts instead of their own. After that, iTunes Connect was shut down for about 4 hours before silently coming back up as if nothing had happened

And:

There was naturally lots of speculation on exactly what the issue was. I think the most likely is something I saw Padraig Kennedy speculate on, that what people were seeing was a staging/test system (maybe for Analytics?). However, even if the data was not editable it does appear to be real data, with real unreleased apps/app versions and real revenue (we’re seeing revenue information for another developer’s apps in AppFigures). Whichever way you look at it, this was a serious bug/issue.

Mistakes happen, but important to know what happened and why, more important to know the extent of the leakage. Was real data exposed? Hopefully, we’ll hear more about this from Apple.

UPDATE: Dave Verwer updated his post:

I’ve been in contact with AppFigures and it does seem that revenue was not leaked into AppFigures. We had another iTunes Connect account that had been added to the AppFigures account and we had not noticed these apps before (it’s on a big AppFigures account and we were checking for strange data this morning specifically after last night’s events). My apologies for not investigating this part of the above thoroughly enough before writing about it.

From Dave’s tweet to me: “The only bit I got wrong was to say that revenue was being reported to AppFigures.”