The number of infections from Trojans, keystroke loggers and system monitors tripled during the last three months of 2004, a security audit has revealed.

According to the 2004 Spy Audit conducted by ISP Earthlink and online privacy firm Webroot Software, the instances of spyware infections on consumer PCs rose 230 per cent, while the instances of Trojans rose 114 per cent from October 2004 to December 2004.

During the fourth quarter of 2004 1,390,883 Spy Audit scans were performed on consumer PCs, detecting 33,096,255 instances of spyware, adware or other forms of potentially unwanted software.

The instances of system monitors in the fourth quarter of 2004 rose from 48,260 in October to 159,262 in December. Trojans in the fourth quarter rose from 55,228 in October to 118,043 in December.

Spy Audit recorded a yearly total of 116.5 million instances of spyware, adware or potentially unwanted items. An average of 25 traces were found per Spy Audit scan for 2004.

"The huge increase in the presence of system monitors and Trojans on consumer PCs is extremely disconcerting," said David Moll, chief executive at Webroot.

"These results are due in part to a substantial increase in the number of recently developed system monitors and Trojans that have been added to the Spy Audit, as well as the continuing infection rate as viruses, worms and freeware continue to propagate and install spyware."

The study warned that Trojans and spyware are capable of capturing keystrokes, online screenshots, and personally identifiable information like social security number, bank account numbers, logins and passwords, and credit card numbers.

"The audited numbers from the past year clearly show that spyware is rapidly becoming one of the internet's most dangerous threats," said Matt Cobb, vice president of core applications at EarthLink.

The complete report is available from EarthLink here.