Spamhaus, a major anti-spam group has been under attack for several days.  The scope of this attack is shared in following article:

http://www.bbc.co.uk/news/technology-21954636

QUOTE: Spamhaus, a group based in both London and Geneva, is a non-profit organisation that aims to help email providers filter out spam and other unwanted content.To do this, the group maintains a number of blocklists – a database of servers known to be being used for malicious purposes.

The attackers have used a tactic known as Distributed Denial of Service (DDoS), which floods the intended target with large amounts of traffic in an attempt to render it unreachable. In this case, Spamhaus’s Domain Name System (DNS) servers were targeted – the infrastructure that joins domain names, such as bbc.co.uk, the website’s numerical internet protocol address.

Mr Linford said the attack’s power would be strong enough to take down government internet infrastructure. “If you aimed this at Downing Street they would be down instantly,” he said. “They would be completely off the internet.”  He added: “These attacks are peaking at 300 Gbps (gigabits per second).

The knock-on effect is hurting internet services globally, said Prof Alan Woodward, a cybersecurity expert at the University of Surrey.”If you imagine it as a motorway, attacks try and put enough traffic on there to clog up the on and off ramps,” he told the BBC. “With this attack, there’s so much traffic it’s clogging up the motorway itself.”

Arbor Networks, a firm which specialises in protecting against DDoS attacks, also said it was the biggest such attack they had seen. “The largest DDoS attack that we have witnessed prior to this was in 2010, which was 100 Gbps. Obviously the jump from 100 to 300 is pretty massive,” said Dan Holden, the company’s director of security research.