Spyware programs that monitor users' surfing habits remain prevalent, but their frequency is on the decline, according to a recent academic study (PDF). Security researchers at the University of Washington used web crawler technology to discover that around one in 20 executable files (5.5 per cent) offered for download on the net during a five month period contained some type of malware, mostly less malign code that generated invasive pop-up ads rather than more dangerous key-logging software.

At the start of the May 2005 survey, 5.9 per cent of sites surveyed attempted to use security exploits to download spyware onto potentially vulnerable PCs. This figure for so called drive-by downloads dropped to 0.4 per cent by October 2005. Warez sites that offer pirated software topped the list for drive-by downloads (4.3 per cent of domains), with celeb sites (3.9 per cent) coming a close second. Although the density of scripted attacks dropped between May and October last year, spyware remains a substantial problem, the Washington researchers conclude.

Spyware and adware programs covertly install themselves on users' PCs in order to serve sneaky pop-up ads or install tracking software to spy on users' surfing habits or, in the worst cases, steal personal information, such as credit card or Social Security numbers. ®

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