It's been a good year for cybercrooks, especially those with the foresight to have gotten in on the boomingTrojan horse business.

The number of new worms, viruses, and Trojan horses jumped 48 percent in 2005, a security company said Tuesday, as it detailed the year's security woes.

U.K.-based Sophos detected nearly 16,000 new threats from January to November, 2005, a major bump from the 10,724 during the same period in 2004. Every month in 2005 posted larger-than-last-year numbers, but November, which was marked by the debut of a strong Sober.z worm, outpaced all others. By Sophos' records, 1,940 new viruses, worms, Trojans, and spyware threats were spotted last month, its largest-ever monthly increase. If that pace were to continue, the next 12 months would see a whopping 23,000 threats.

Topping Sophos' top-10 chart was the long-running Zafi.d, a mass-mailed worm that made itself known almost a year ago: It accounted for 16.7 percent of all threats detected during the first 11 months of 2005. Netsky.p took second place, with 15.7 percent, while the new Sober.z came in at third, with six percent.

"Given more time, Sober.z would have dominated the chart, but its emergence in late November prevented it from taking pole position," said Graham Cluley, senior technology consultant at Sophos.

But it's not the threats that make national news that has Cluley, and other security experts, worried.

"Trojan horses are the real growth area," said Cluley. Sophos' report noted that new Trojan horses outnumbered Windows-oriented worms and viruses by almost 2:1. In 2005, Trojans accounted for 62 percent of all threats, while Windows worms made up 35 percent of the total.

"This [overall] increase stems from the escalating interest in authoring Trojans by criminal gangs intent on making a profit," said Cluley. "By focusing their efforts on a smaller number of victims [with Trojans], cybercriminals can increase their chances of slipping under the security net.