Almost one in five emails delivered in Ireland during October was found to contain a malicious virus, according to e-mail hosting company IE Internet.
The figure is the highest recorded infection rate since IE Internet first began monitoring email activity in October 2003.
The rise in virus infections has been attributed to a number of older viruses which have been gaining new ground in recent months. The Mytob worm was the most prevalent virus last month with variants of the worm collectively responsible for almost half of all virus infections.
The Mytob worm allows infected machines to be controlled by remote users for criminal purposes such as sending out millions of spam emails.
IE Internet's technical manager, Ken O'Driscoll, warned that infection rates are likely to continue climbing if people continue to fall for the "social engineering techniques" designed to trick users into opening attachments.
Many spam e-mails carry titles promising cash windfalls or easy weight loss to attract gullible users.
Meanwhile, the US remains the largest producer of Spam worldwide and is responsible for over 40 per cent of all spam emails delivered in October. South Korea remains the second largest purveyor of spam emails and contributed over 7 per cent of total spam in October.
Spam emails accounted for 43.83 per cent of email messages delivered during September but this decreased to 37.83 per cent in October.
Korea has the highest Internet broadband penetration in the world allowing spammers to take advantage of its high-speed connections.