Just like the T-Mobile Dash Windows Mobile 6 Upgrade was leaked about a week before the real release, AT&T's 8525 update has just been dumped onto the internet as well. What does this mean to you? Two things.
One, the official official (meaning residing on AT&T's servers) will be upon us soon. Two, you're probably safe installing this on your phone, since it's going to be (most likely) the same ROM as the one being released soon. Happy upgrading.