According to monitoring by anti-spam filtering firm Brightmail, during the last five years the incidence of spam attacks has rocketed from a few hundred a month to nearly 7.5 million in May.

The company said that, in April 2001 seven per cent of the email it checked was spam. As of June 2003, it found over 48% of all email traffic on the internet is unsolicited.

In addition Brightmail said its monitoring has revealed that spam email in the UK is rapidly becoming more offensive.

In June, over 20% of spam was pornographic - now the second largest UK spam category, following 34% of email spam that offers products for sale.

In the US only 19% of spam fell into the adult-content category in June.

Speaking at the UK Spam Summit in Parliament, Enrique Salem, chief executive, Brightmail said: 'No one thought that spam would be the primary use of email. So they did not have solutions built in to provide better security. The spam we saw six months ago is not the spam that we see today. We are in an arms race.'

Enrique believed the spam problem would be 'under control in the next three years', provided there is combined efforts from internet service providers, technology companies, legitimate direct marketing firms and legislation.

While the volume of adult spam is disturbing, the largest category of unsolicited spam continues to come from illegitimate direct mail companies that offer products to email users who have not requested to be contacted.

Stephen Timms, minister for energy, e-commerce and postal services, said that the government recognised that spam was a growing problem, and one that could put people off using the internet.

'This is an area where there are huge problems and great frustrations. But it is an area where there are solutions as well. We don't want to suggest spam will disappear, but well thought through regulation, industry action and user awareness can help make big inroads.'