Spamhaus, a Geneva and London based group which weeds out unsolicited "spam" messages for email providers, has been targeted by a Dutch web host in retaliation for being blacklisted. Cyberbunker, which says it will host anything with the exception of child pornography or terrorism-related material, has accused Spamhaus of abusing its position, claiming it should not be allowed to decide what goes onto the internet. The row is causing an internet slowdown and experts are concerned the attacks could soon escalate and start to affect banking and email systems. Paul Vlissidis, group technical director at internet security firm NCC, said the fact that lots of computers were involved in the attacks on Spamhaus made it much harder to defend against them. If you have a few computers sending large amounts of traffic you can filter them out easily. When literally thousands and thousands are involved it makes it much, much harder," he said.