Spammed Trojan horses accounted for more than 7 out of every 10 new threats that users faced in August, a security company said Friday.
U.K.-based Sophos' tally of the month's malware showed that 71.8 percent of the new malicious code was Trojan. The company spotted nearly 2,000 new exploits during August.
Rival security firm McAfee confirmed the trend toward one-off Trojans -- which don't replicate on their own, or infect other systems via new malicious e-mail messages -- and a corresponding decrease in traditional worms.
Rather than spread slowly, as worms often do, Trojans are increasingly blasted out in high-volume, short-lived spam campaigns. "Spam runs of these [Trojans] occur within just a day, or at the most, two," said McAfee in an online research note. "This gives the spammer enough time to reach a multitude of inbox[es], and just enough time before the majority of AV [anti-virus] vendors can release signatures to detect the new critter."
McAfee highlighted three recent Trojans -- Yabe.r, Dloader.dhx, and Haxdoor.il -- and graphed their rapid rise and fall. The first was spammed into users' inboxes in a two-day period of July 4-5, while the other two each came and went within a day.