WikiLeaks, famous/infamous for its releases of classified documents pertaining to the Iraq and Afghanistan wars, is under attack.
WikiLeaks is about to release its largest set of documents pertaining to the US, and this release may be its most scathing yet. The release is likely to cover cables/documents related to nearly every country in the world, and some are likely to be embarrassing. Secretary of State Clinton has already begun a blitz of apologies and preparations for the release.
The DDoS attack may be an attempt by one of any number of US agencies (CIA, NSA, DoS, etc), or any other pro-American group. Certainly, WikiLeaks has made a number of enemies in the past few years, and has even lost the immunity it used to enjoy in a few countries in Europe.
In the end, such a DDoS is far too late. WikiLeaks is an intelligent organization, and has many outlets by which it can share its (backed up many times over) data, including the New York Times and the Guardian.
Thus, I'm not entirely sure what the DDoS is driven by, except as a lash-out or retaliation. WikiLeaks' paranoia means it will require a much more sophisticated attack to have any hope of taking it down.