It's not clear in fact whether it's some outside hack or whether it was an internal leak. The weight of the evidence so far seems in favour of the 'whistleblower' theory. I'm sure the employees at UEA CRU would really like to know for sure.
The rest of your argument is a moot point now, as the UEA CRU has now issued a statement that it will release all data and methods (who knows when). Your forgetting (perhaps conveniently, you say you are a familiar with the scientific process after all) that the heart of this issue is the issue of replicability, that any claims being made by scientists are worth nothing unless they can be properly replicated by an independent means. Any claims/data which are being kept secret means that other scientists cannot verfify those claims- and therefore those claims must be automatically assumed to be false.