Screenshot
Tonight, Apple confirmed the outage was due to a hack. The hacker apparently attempted to access personal information about the developers.
Here's the statement from Apple:
Last Thursday, an intruder attempted to secure personal information of our registered developers from our developer website. Sensitive personal information was encrypted and cannot be accessed, however, we have not been able to rule out the possibility that some developers’ names, mailing addresses, and/or email addresses may have been accessed. In the spirit of transparency, we want to inform you of the issue. We took the site down immediately on Thursday and have been working around the clock since then.
In order to prevent a security threat like this from happening again, we’re completely overhauling our developer systems, updating our server software, and rebuilding our entire database. We apologize for the significant inconvenience that our downtime has caused you and we expect to have the developer website up again soon.
It's important to note that the hack probably won't affect the average customer, only those with paid developer accounts. However, it does come at a time when Apple is putting the finishing touches on its new operating system for iPhones and iPads, iOS 7, and its new operating system for Macs, OS X Mavericks.