
The security firm warned that the most notorious threat remains the Tibs worm, otherwise known as Storm Worm, accounting for 3.91 percent of all detections.
Fortinet added that, according to its monitoring, no fewer than 36 variants of the Storm Worm have been active this month, although one variant accounted for nearly 60 percent of related detections.
Storm Worm continues to have a severe impact on mailboxes worldwide, according to Guillaume Lovet, EMEA threat response team leader at Fortinet.
"The overwhelming presence of the Storm Worm is not without consequence, as it is being used to generate and relay massive amounts of spam," said Lovet.
"However, the battle against spam is not lost. A purely factual analysis tends to prove that spammers are losing ground in the final race to arms against content analysis filters."