UK and Switzerland-based nonprofit organisation Spamhaus, which operates a filtering service, has been hit by distributed denial of service (DDoS) attack, which several security companies claim is the largest DDoS to date.

Spamhaus chief executive Steve Linford said that the company has been under this cyber-attack for more than a week.

"They are targeting every part of the internet infrastructure that they feel can be brought down," Linford added.

Security firm Kaspersky Lab confirmed the attack and claimed it was the largest DDoS cyber attack. Kaspersky Lab said: "Based on the reported scale of the attack, which was evaluated at 300 Gigabits per second, we can confirm that this is one of the largest DDoS operations to date. There may be further disruptions on a larger scale as the attack escalates."

The cyberattacks on Spamhaus started when it added the Netherlands-based web hosting firm, Cyberbunker, to its global blacklist.

According to a CloudFlare blogpost, the attack was initially approximately 10Gbps generated largely from open DNS recursors on 18th March, while on March 19, the attack increased in size, peaking at approximately 90Gbps.

The attack fluctuated between 90Gbps and 30Gbps until 01:15 UTC of March 22.

A DDoS attack is an attempt to make a machine or network resource unavailable to its intended users, most commonly by saturating the target machine with external communications requests.

Earlier this year, Gartner predicted that the number of sophisticated attacks on e-commerce and financial industries will increase in 2013. The research firm expects that high-bandwidth DDoS attacks will become the new norm and be particularly damaging to unprepared enterprises.