Update: seems to back to normal.
Its a site where people can register and post pictureblogs. If I register as ryan the adress to my page would be ryan.bilddagboken.se.
After YEARS of running the place (around 800.000 users) someone registered the username "www". This resulted in all visitors that typed www.bilddagboken.se (or used a bookmark) was directly redirected to the user "www" page. His/Hers page had thousandths of angry comments accusing him/her of hacking bilddagboken.se
paulphusion: @posterous Something went wrong yesterday when I tried to forward my own url to my posterous account. I'm sorry! What was the reason? 17 hours ago
paulphusion: @scottgould did I crash posterous? omg! was just trying to forward my domain to my posterous account. I'm sorry! 17 hours ago
Waiting for the official post, i'd say that Paul misconfigured something that they didn't test for that particular input.
Like many software bugs, it was an edge case that we didn't foresee, but that happened extremely rarely. We've been running Varnish for the better part of a year, millions upon millions of requests and this was the first time something like this has ever happened.
Of course, none of that wipes the egg off of our face. ;)