October saw a sharp increase in zombie activity and spam levels as criminals target users in the weeks before Christmas, a new report revealed today.

According to the MessageLabs Intelligence Report, October saw spam emails jump to 73 per cent - an increase of eight per cent on the previous month - and the sharpest rise in spam levels since January this year.

Security professionals believe last month saw a sudden growth of botnet activity and spam, as cyber criminals prepare to attack recipients in the months before the festive celebrations.

The research found that a Trojan - SpamThru - is responsible for the sudden rise in zombie commands and unsolicited email, with three out of four emails last month found to be spam.

The study states that hackers have employed several tactics to avoid detection in email filtering systems. The spammers released new strains of the Trojan at regular intervals to confuse anti-virus detectors. Moreover, they used a template for each email sent and combined it with a list of email addresses, enabling the zombie to dispatch millions of spam messages.

The report states that another contributor to the rise in unwanted email was the Trojan dropper - Warezov - which researchers claim is "one of the most aggressive Trojans seen this year". An initial strain was released in August, but the virulent batch was sent on the 26th October. According to the report spammers released several strains, each containing a different code to allow the Trojan to evade detection in anti-virus filters.

Mark Sunner, CTO at MessageLabs said: "In recent months, the focus has predominately been on targeted virus attacks and spam has hardly received any attention.

"However, with the arrival of SpamThru and Warezov it looks as though the bad guys have been honing their skills and are now in full force with new techniques to dupe protection resources."

He continued: "As seen in previous years, we expect spam levels to continue to rise during the coming weeks and months as the spammers intensify their efforts around [Christmas]."