The sun seems to be having an inspiring effect on the world's spammers, with levels of pornographic spam rising in step with the temperature. According to Clearswift's monthly spam index, the amount of porn being sent to our unsuspecting inboxes has risen 350 per cent since June.

The company's spam watchers also noticed a distinct increase in the amount of mails touting cheap Viagra, and suggests this might be "an attempt to match supply with demand".

Joking aside, Alyn Hockey, the company's director of research, says that the influx of smut needs careful management. He argues that it is not just that companies' reputations can be compromised by porn emails circulating un checked, but that porn is also a popular carrier for malicious code. Even in the virtual world unprotected sex is a dangerous business.

The surge of porn spam in summer does appear to be a recurring phenomenon: Clearswift noticed similar increase last year. By contrast, spammers hawking diet pills are the busy ones in the winter.

Overall, however, the pornography is a relatively small slice of the spam pie: financial spam accounts for 39 per cent of the rubbish clogging our inboxes, with healthcare mails a close second with 30 per cent of the 'market'. Porn accounts for just under five per cent, and scam mails just one in every hundred messages. ®

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