Netsky-P topped the list of most prevalent viruses and hoaxes during October, according to a report.
A report from software company Sophos found that Netsky-P had continued to top its chart of most prevalent viruses and hoaxes since June.
Also in the top five last month were Zafi-B, followed by Netsky-D, Netsky-Z and Bagle-AA. According to a statement from Sophos, Zafi-B has also topped the company's chart since June.
Sean Richmond, senior technical consultant at Sophos Australia/New Zealand, said that despite protection against Netsky-P and Zafi-B being available, there were "thousands of their infectious email offspring traversing the net".
"This suggests a large base of out of date or unprotected machines continuing to cause problems for the rest of the computing world. With the exception of Bagle-Zip, every entry in the top 10 has been detectable for several months," Richmond said.
Sophos found one in every 22 emails circulating last month was viral, according to the statement.