More than one in every three e-mails sent to Irish e-mail accounts last year was identified as spam, an increase of 10 per cent over 2004, a study by security group IE Internet shows.

The overall trend increased significantly on previous years, with an average of 38 per cent of all e-mails being identified as spam in 2005, the group said in its annual report.

The rise can most likely be attributed to an increased use of broadband and people spending more time on the internet, the group said.

The US was the worst culprit when it came to the source of spam e-mails, with some also originating in Britain, China and Europe. IE Internet said that one of the most interesting developments last year was the appearance of South Korea as one of the emerging sources of spam.

The worst month for spam in 2005 was June, when the rate of spam exceeded 41 per cent. This was an increase of more than 100 per cent on the figure reported for June 2004.

However, while spam e-mails are a significant problem for businesses, costing large sums of money in protective software, they are not the only internet-related problem that businesses have to deal with.

IE Internet's research also found that about 12 per cent, or one in every eight e-mails circulating last year, contained a virus. Many of these viruses can, in turn, be passed very quickly and easily from one computer to another.

When compared with 2004, the overall number of virus-infected e-mails increased by three percentage points.

The most common virus strain detected last year was Netsky.P, a worm that entices the recipient to open what appears to be a failure notification of an e-mail message that they have sent. It is capable of disabling commercial anti-virus software.

Zafi.D was the second-most prevalent virus last year, according to IE Internet, which is predicting that this virus will remain a real threat for at least the first quarter of this year. Zafi.D spreads via the internet as an attachment to infected messages and, once launched, copies its file to the Windows system directory and allows it to run every time that the system is started.

IE Internet is also forecasting as inevitable an increase in viruses designed to attack mobile communication devices. The group said that the growth of mobile computing is threatening to undermine traditional virus protection.

Portable software devices such as palm pilots may in the future be used to transport viruses, it said.

It also forecast an increase in so-called "phishing" attacks, whereby criminals seek to defraud banking customers by gaining access to their personal information.

IE Internet monitored 15,000 Irish businesses over the past 12 months.