According to research from anti spyware firm Webroot Software and ISP EarthLink, 500,000 system monitors and Trojan horses were discovered from 1.5 million spyware scans completed.
Approximately 41 million traces, at an average of 27.5 per machine, were found.
"The SpyAudit's popularity shows that consumers want to find out what is on their computers," said David Moll, Webroot's CEO. "Based on the overwhelming number of spyware traces identified in just four months, we urge consumers to run an audit as soon as possible to determine if they have spyware on their PCs and then take action to manage it."
System monitors and Trojan horses are two types of spyware applications. System monitors are designed to keep track of a consumer's computer activity and can record virtually everything a user does online. Trojan horses are applications that appear as requested software programs, but facilitate theft of computer data by permitting hackers to gain unrestricted access to computers while web surfers are online.
The SpyAudit report charts the overall number of scans and figures for each of the defined spyware categories from January 1, 2004 to April 30, 2004.