I'm shocked that anyone's emails can end up in a cache on the internet, tbh.
Ive just asked DH about this, cos I don't understand this stuff.
His response was that Google can't find things (to put on its search engine) unless there are links to that forum to somewhere else on the Internet. It doesn't have to be to that sensitive data just to the forum its on (which has to be public not locked down). It also has to be a public link to a site that is indexed by Google.
It suggests that level to which the information was publicly available (through Google) and the lack of any form of security.
He suggests that this information was already being shared on another website before Mermaids deleted their directory and had been shared for a while as Google does not magically index things overnight.
It's not someone archiving it privately. It's a link which someone created and shared publicly.
His concern would be what sharing and linking created the cache.
That's about as much as he can work out, but it's a big deal that there was a cache at all. This was supposed to be a forum that was totally private and to only be accessed by the Trustees and Susie Green from the information we have about the forum.
It either suggests one of those authorised to view the forum shared it (but they all believed it was private so why would they?) Or someone else found it some time ago and shared it. (Which also rules out the Times as they had no reason to share publicly and they also had an understanding of sensitive nature of that information)
The information shared that I know is 'in the wild' was shared after the directory deletion and was from the cache. So it's not that either.
This leaves a mystery as to who it was and suggests this information has been 'wild' for some time at an unknown public source. It suggests an unknown party or parties we do not know about.
Which should only add to the concerns of anyone who has had their data leaked.