There are an average of 28 spyware programs running on any given computer, according to a survey by ISP Earthlink and Webroot Software. Worse, Trojan horse or system monitoring programs were found on more than 30 percent of all the systems scanned.

While the report may need to be taken with a pinch of salt as Webroot makes its living selling software that locates and removes spyware, plus it and Earthlink have a long business history, it nevertheless claims to be the result of scans of over one million Internet-connected computers.

The vast majority of the 29 million spyware programs found were harmless "adware" programs that display advertising banners or track Web surfing behaviors. However, the companies also found more than 300,000 instances of programs that are capable of stealing personal information or providing unauthorised access to computers, the companies said.

Spyware is a generic term that describes a wide range of programs that track user behaviour on a computer, often for marketing purposes. The programs are sometimes bundled with other software, such as peer-to-peer file sharing programs, and installed legally on users' systems. However, once installed, they run surreptitiously in the background and can be difficult to detect and remove.

The report covers the first three months of 2004 and compiles information from scans conducted by both EarthLink and Webroot. It is the first of what will be regular updates that track the prevalence of spyware, the companies said. The results show the proliferation of spyware and should encourage computer users to take steps to protect themselves from spyware, according to a joint statement.

In particular, the detection of over 184,000 Trojan horse programs on the systems scanned and a similar number of system monitoring programs, such as key-logging software, underscore the potential for identity theft and system compromise for Internet users, said Matt Cobb, EarthLink VP of core applications.

The Atlanta-based ISP began offering spyware protection for customers in October. EarthLink added a program called Spyware Blocker for free as part of its TotalAccess package of software programs and tools, which EarthLink subscribers can download from the company's website.

Spyware is gaining greater attention from software companies as well as lawmakers. In recent months, anti-virus companies, including Network Associates have released anti-spyware products. Also, in February, a group of US senators introduced the Software Principles Yielding Better Levels of Consumer Knowledge (SPYBLOCK) Act, which would prohibit installing software on somebody else's computer without notice and consent and outlaw the use of "any information collection, advertising, distributed computing, or settings modification feature" that's installed without consent of the computer's owner.