Jim Dalrymple spoke with someone at Apple on their email to developers that the site was hacked:

The only thing that the hacker could have gotten access to was the names, email addresses and mailing addresses of the developers. At this point, Apple doesn’t know if the hacker even managed to see that information. Worse case, that is all the information they would have seen, according to Apple.

Apple has taken the developer site offline and is working to get the site secured before re-launching it. The company had no timetable for when that might happen.

When the site went down and wasn’t restored in two or three days, people suspected a hack. It sucks but if we’re to believe Apple, it doesn’t seem too bad. And as much as I applaud them for waiting to get the system fully secured before bringing this up, it took a while for them to respond.

If a hack happens and you don’t know how or what was accessed, I’d rather you say that than leave people to guess. Hopefully they’ll get it working soon and it won’t impact the Mavericks or iOS 7 beta release schedules too much.