The attack started at 09:00 BST and lasted till 14:00 BST, it was launched from a botnet of compromised Windows PCs, the traffic was directed at the web servers for Spamhaus.

Director of the Spamhaus project Steve Linford explained that the site was brought back into operation after technical staff setup filters to null route the offending traffic. This, is not the first attack against Spamhaus, in September 2003 machines compromised by the SoBig worm where used to launch attacks against Spamhaus and other anti-spam organisations. Some of the smaller organisations at the time didn't survive. The perpetrator of this attack is not known at this time.

These kinds of attacks against anti-spam sites are not uncommon, however they are usually more low key.