I'm using Windows 7. I moved the wallet.dat to my mac and it's encrypted too.
I'm not sure because it was a few months ago, but I think I've downloaded from the original website. I installed it only once.
I'm trying to think if I encrypted the wallet and no remember that, but the thing is that I didn't have it in my mind and last week I've tried to encrypt it and couldn't because the menu was grey. I also tried all the passwords I could ever put with no results.
Three months mining and now i've got nothing