It would also include MAPS' Relay Spam Stopper, which lists unsecured relays that have been used to transmit spam.

CNN: Next wave of attacks against spammers underway

To block spam, large ISPs and corporations use a multitiered system of filters, lists of known spammer addresses and sometimes even staff who can recognize incoming spam and thwart it manually.

FORBES: Spam Warfare

To block spam, large ISPs and corporations use a multitiered system of filters and lists of known spammer addresses and sometimes even staff who can recognize incoming spam and manually thwart it.

FORBES: Spam Warfare

Non-profit Spamhaus maintains what are known as "block lists" which many organisations use to spot sources of spam and other junk mail to stop them clogging mail servers and inboxes with unwanted messages.

BBC: Dutchman arrested over huge web attack

While the technique of routing mail via mail servers of net service firms might cause problems for those that use blacklists and block lists it did not mean that other techniques for stopping spam lost their efficacy too.

BBC: PC hard drive, Eyewire