The speed of which it was able to spread comes from Tumblr’s Reblog feature, which is pretty much the same as Twitters Retweet function. The post spread across accounts warns that the users account will be deactivated if they do not reblog the message. Hard to believe that people will fall for that, but they did and in great numbers.
Tumblr is testing for inactive blogs so the URLs can be deleted and reused by new members In order to not lose your blog, you must reblog this post so that your name will be on the safe list.
Thank you for your cooperation,
David Karp, CEO