Keeping an eye on this. The post in question looks like this:
https://dl.dropbox.com/u/58607934/Screen%20Shot%202012-12-03...
It has nailed a number of major accounts, including The Verge, USA Today, Reuters and The Daily Dot.
Buzzfeed has tips on how to keep safe: http://www.buzzfeed.com/ryanhatesthis/hacker-group-exploits-...
Update: The GNAA says that the hack was part of an anti-blogging campaign.
> This was just another part of our "anti-blogging" campaign. GNAA's stance on blogging in general has always been a negative one: in short, blogging is lowering journalistic standards to the point where the number of friends a murderer has on Facebook has become news.
http://www.guardian.co.uk/technology/2012/dec/03/tumblr-cybe...