Volumes of pornographic spam have tripled during the past month, newly published research has revealed.

According to data from email management company Email Systems, pornographic spam has rocketed from seven per cent of all unsolicited mail in December to 21 per cent in January.

Overall the firm reported that spam emails have risen by around 40 per cent since November, while virus traffic has steadily declined. Spam now accounts for around 90 per cent of all email.

The research also indicated that more than two in five spam emails are medically related. In contrast, spam advertising financial services dropped from 21 per cent of all spam in December to just 10 per cent in January.

Email Systems managing director Neil Hammerton said: "January is clearly a month when consumers are less motivated to purchase financial products or put money into dubious financial opportunities.

"Spammers seem to have adapted their output to reflect this, focusing instead on medically motivated and pornographic offers, presumably intentionally intended to coincide with what is traditionally considered to be the bleakest month in the calendar."

Email Systems said that denial of service (DoS) attacks using email are also increasingly frequent. One of its clients in the engineering sector received 12 million emails during January, of which only 54,000, or one in 200, were legitimate.

"The increasing frequency of DoS attacks means that it is no longer just the multinational corporations that are on the receiving end," said Hammerton.

And despite several surges where virus email accounted for 15 per cent of daily email traffic, virus traffic has steadily slowed since the beginning of November.

"It is interesting to note that viruses are currently in a downward trend, but of course virus attacks are by their nature entirely unpredictable so this could change dramatically from one month to the next," said Hammerton.