Digital direct: Spammers render blacklists useless in 'zombie' attack

May 09, 2005

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Digital direct: Spammers render blacklists useless in 'zombie' attack

An estimated 75 per cent of all email sent over the internet is 'spam'. This is predicted to rise to 95 per cent by 2006 if nothing is done. The problem is a little-publicised breach of one of internet service providers' (ISPs) primary defences against junkmail blacklists, which they use to block emails from known spammers. Since their introduction, blacklists have helped to reduce spam by about 10 per cent, but the ever-resourceful spammers have devised a ruse that renders them ineffective.

The most recent version of Send-Safe - the software used by many spammers - is the first to help exploit the new technique. It helps take control of broadband-connected PCs - which become known as 'zombies' - and uses them to send emails. Since this activity happens in the background of the 'zombie' computer, users are unlikely to be aware there is a problem.

It is reported that around 80,000 to 100,000 new PCs are being infected per week, and nearly 70 per cent of all spam is sent via this method - that's more than 50 per cent of all email sent.

So, how does it circumvent ISPs' blacklists? Hitherto, blacklists have recorded addresses of spamming computers, but now Send-Safe disguises the origin of the spam to make it appear that it's coming from the zombies' ISPs instead of infected machines. In the weeks since the latest version of Send-Safe was released, email-filtering firm Messagelabs has reported a rise in the level of email it handles. It's too early to tell whether this is due to Send-Safe or just an aberration. But, anti-spam organisation Spamhaus predicts that, unless action is taken now, 95 per cent of the world's email will be spam by the middle of 2006.

Nicholas Mann is managing director of Interdirect

See Analysis, p21.

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