( CNN ) -- Internet users around the globe are facing slowed-down service , thanks to what 's being called the biggest cyberattack in history . The prolonged denial-of-service assault is targeting The Spamhaus Project , a European spam-fighting group that has gone after CyberBunker , a data-storage company that offers to host any content `` except child porn and anything related to terrorism . '' The organization has been in a long-running feud with CyberBunker and claims spammers use it as a host from which to spray junk mail across the Web . Internet security firm CloudFlare said Spamhaus contacted it last week , saying it had been hit with an attack big enough to knock its site offline . Security experts say the attack uses more sophisticated techniques than most DDoS ( distributed denial of service ) attacks and targets the Web 's infrastructure , which has led to other sites performing slowly . `` It 's the biggest attack we 've seen , '' Matthew Prince , CloudFlare 's CEO , told CNN . The FBI is involved in the investigation into the cyberattack on Spamhaus , though a bureau spokesman did n't provide any details on the FBI 's role or the scope of the probe . The Spamhaus Project is a nonprofit organization that patrols the Internet for spammers and publishes a list of Web servers those spammers use . According to Prince , the group may be responsible for up to 80 % of all spam that gets blocked . This month , the group added CyberBunker to its blacklist . `` While we do n't know who was behind this attack , Spamhaus has made plenty of enemies over the years , '' Prince wrote in a blog post . `` Spammers are n't always the most lovable of individuals , and Spamhaus has been threatened , sued and DDoSed regularly . '' In a DDoS attack , computers flood a website with requests , overwhelming its servers and causing it to crash or become inaccessible for many users . One way to defend against those attacks , Prince said , is to deflect some of the traffic targeted at a single server onto a bunch of other servers at different locations . That 's what happened in this case , and why Web users experienced some slowdowns on other sites . He told CNN the last big wave of the attack hit Tuesday morning , but that he does n't `` live under the illusion '' that there wo n't be more . For its part , CyberBunker is n't taking credit for the attack . But the Dutch company , housed in a former NATO nuclear bunker , is n't shying away , either . `` This here is the internet community puking out SpamHaus , '' CyberBunker founder Sven Olaf Kamphuis told CNN . `` We 've had it with the guys ... . What we see right here is the internet puking out a cancer . '' He said the owners of various websites got together on a Skype chat and hatched the plans for the attack . He says that StopHaus , a group organized to support CyberBunker in the dispute , ceased the attack after three days but that other hackers and activists kept it up after that . Kamphuis and other critics say that Spamhaus oversteps its bounds and has essentially destroyed innocent websites in its spam-fighting efforts . `` Spamhaus itself is a more urgent danger '' than spam , Kamphuis told CNN . `` Pointing at websites and saying they want it shut down and then they get it shut down without any court order . That is a significantly larger threat to internet and freedom of speech and net neutrality than anything else . '' Vincent Hanna , a researcher with The Spamhaus Project , said the group 's record speaks for itself . He said the project has existed for over 12 years and its data is used to protect more than 1.7 billion e-mail accounts worldwide . `` We have 1.7 billion people looking over our shoulders to make sure we do our job right , '' he said . `` If we start blocking things they want , they wo n't use our data any more . '' He emphasized that Spamhaus does n't have the power to block e-mail from anyone -- it merely makes its data available for service providers and other Web companies to use . Hanna said Spamhaus experienced its first denial-of-service attack in 2003 . `` This has been the biggest for us , '' he said , `` but certainly not the first one . '' Cloudflare 's Prince said denying access to a website through cyberattacks is the truest assault on Web freedom . `` Our role is to allow the internet to achieve what it aspires to -- that anyone , anywhere can publish any piece of information and make it accessible to anyone , anywhere else in the world , '' he said . `` It 's blatant censorship . `` Whether Spamhaus is a good organization or a bad organization is irrelevant to me . We protect American financial institutions , which some people think are evil , and we protect WikiLeaks , which some people think are evil . '' CNN 's Atika Shubert , Antonia Mortensen and Terry Frieden contributed to this report .
NEW : The FBI is involved in the investigation into the cyberattack , a spokesman says . A massive cyberattack is creating ripple effects for Internet users around the globe . The prolonged denial-of-service assault is targeting Spamhaus , a European spam-fighting group . Security expert : ` We have seen this kind of thing before'- said one security researcher who has been working on the case.