Responsibility for Sunday's attack was claimed by a single hacker, the Jester, though many are skeptical that it was the work of just one person.
Today's attack, which was initially focused on http://cablegate.wikileaks.org/, has been much more intense. At 9:00 a.m. ET, WikiLeaks tweeted, "DDOS attack now exceeding 10 Gigabits a second."
As Fast Company notes, that's much stronger than the 2 to 4 gigabits per second of Sunday's attack. Security firm Netcraft has been following today's attack, noting that it was expanded to include the main wikileaks.org domain as well.
In North America, access to the site has been relatively unencumbered. Fast Company details that the bulk of the attack took place during the European business day.
The decentralized nature of WikiLeaks and the fact that the documents in question are available on the web via torrents makes the impact of these attacks largely one of annoyance. In other words, even if hackers do manage to take down the website itself -- the information is still accessible via alternative channels.