Netsky-P worm continued to head up the top ten chart twenty months after it was first detected, accounting for 17.2 percent of all infections. However, Mytob-GH, which first appeared just over two weeks ago, was found to have already reached second place (8.1 percent) and showed no sign of abating. This Mytob variant is well placed to topple Netsky-P from the top of the chart in November, according to the IT security firm.
Sophos reported that a brief lull in virus activity during September has been short lived. Two thirds of October's record count was attributed to versions of the Mytob worm, with the newly discovered Mytob-GH and Mytob-EX variants having made a significant impact.
"The unfortunate onslaught of new threats this month is unsurprising as malware authors ramp up their game in their pursuit of hard cash," said Carole Theriault, senior security consultant at Sophos.
"The Mytob dynasty continues to grow - attacking networks thick and fast. This barrage of threats shows no sign of slowing down."
This month's chart consists of only three virus families - Netsky, Mytob and Zafi, indicating that virus writers are continuing to create variants of established threats, which prove most effective for financial gain.
"There are six variants of the Mytob worm in the October chart, half of which are new entries," added Theriault.
"The creators of Mytob appear to be a gang of virus writers called Hellbot. By having several gang members they can easily issue several different variants in a short space of time."
With this rise in viruses, Sophos's research shows that 1.66 percent, or one in 60 emails, circulating in October were viral.