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The U.K. now receives 20 billion spam emails a day, roughly one sixth of the daily global total, filtering company IronPort has said.

According to the Cisco subsidiary's Internet Security Trends report for 2007, this deluge means that each business inbox now receives between 100 and 1,000 spam emails per day, even as the overwhelming majority of these are filtered out by gateways and never seen by users. Overall, spam volumes have doubled in 2007.

IronPort quotes a rather speculative US$500 cost per PC to deal with the problem, with most of this cost hidden in the back office, while users ignore the issue at the desktop level. Even the small amount of spam that gets through equates to each recipient wasting 5-10 minutes per day dealing with a scourge that now consumes 98 percent of all Internet email traffic.

Contradicting the popular view that spam exists solely to hawk unwanted and fraudulent products to the gullible, IronPort's analysis suggests that the motivation has increasingly become to spread malware for a range of other criminal purposes. Such "dirty spam", containing links to malware-spreading websites, grew 253 percent in the last year, the company said.

Today's spam was still dominated by pharmaceutical and stock-pumping scams, which together account for 60 percent of the phenomenon in 2006. Attack types appear to have diversified at an astonishing rate in the last year, rising from the single 2006 innovation - image spam -- to around 20 types of attachment ruse in the last year, including the use of PDFs and MP3 files.

Not surprisingly, IronPort's recommendation is technological, that if using reputation services to blacklist spam sending addresses, despite the fact that such services have so far done little to halt the spam tide. Indeed, the more effective spam filtering systems become, the more incentive spammers have to turn up spam volumes in the hope of maintaining the percentage of spam reaching users.

This battle between spammer and filter showed now sign of abating. "They [spammers] might send out a very limited trial quantity to see how effective the new strain is against spam filters. Once spammers are confident that they have created a content set that will get through most spam filters, they will launch a very large-scale attack," says the report.