Alton is the most spammed town in the UK, according to an analysis by messaging service provider MessageLabs. But why does so much spam head to an innocuous town of 17,000 people in Hampshire?

The 2009 spam top ten reads, in order, Alton, Teddington, Havant, Cirencester, Brighton, Barking, Dundee, Swansea, Bromley, and Marlow. Last year's most spammed town, Egham, is now at number 14. The company also records the towns with the ‘lowest' levels of spam and the winner this year was Fareham, also in Hampshire, followed in second and third place by Lincoln and Wilmslow.

MessageLabs garnered these figures from a 31-day analysis of traffic to its own customer base, which has a bias towards the UK, despite the fact that the company was bought out a year ago by Symantec and has an international reach.

It is worth pointing out that the difference between the least and most spammed towns is actually the difference between places where spam now makes up 87.6 percent of all messages and 97.6 percent of all messages. So even in the best location, Fareham, nearly nine out of ten messages are spam.

Leaving aside a possible concentration of MessageLabs' customer base on the towns mentioned, why would more spam appear to head to one town over another? The nature of spam is its non-directed universality.

A possible explanation turns out to be the fascinating if loose relationship between the number of domains registered to companies in a particular town relative to the size of company involved.

"If you have a domain then the spammer doesn't have to get the bit on the left [the name address]," points out MessageLabs' Paul Wood, explaining the spammer's basic method of attack. "What you [the user] don't see is the mail server receiving and bouncing messages."

Spammers look at email-passing domains, not employee numbers when deciding where to send their junk, and that tends to mean that the smaller an outfit the more spam they will get relative to their numbers because they have more domains for fewer users.

It turns out that a particular ‘sour spot' is for modestly-resourced SMB companies with around 100 real addresses. These companies will have several domains that can be targeted as traffic-passing, will probably have far fewer layers of forward defence than larger companies, and will find more spam hitting their servers as a result. Little of that will reach users, so it remains a hidden overhead to employees.

What matters, however, is not the numbers of employees per se but the number of domains that have to be filtered. 

The exact makeup of the companies in MessageLabs' top ten towns can only be guessed at, but it is noticeable that they congregate disproportionately in an area of southern England to the west of London. So what appears to be a problem for Alton could actually be a problem of the SMB businesses that are particularly dense in the town and its surrounds.

Towns like Fareham, at the bottom of the spam-receiving list, might just have fewer of these domain-hogging businesses. Meanwhile, Egham has fallen slightly off top spot because of recession. It's a theory.

If true, the 'top towns' phenomenon is likely to repeat the world over, and be just another usually hidden pattern in the homogeneous deluge of spam against which millions of nameless machines struggle day in day out, expensively, on and on into the future.