The Register (technology news website) last year quoted a research report from the University of Washington, that revealed 1 in 20 files offered for download in a 5 month data sampling span contained sufficient number of malware. These covertly installed programs pose a real threat to surfers now and browser manufacturers have also started designing updates to stop this threat.
However, the study undertaken by Google researchers brought the issue of Drive-by downloads into limelight. Result shows that around 450,000 URLs actively involved in this malpractice. The study analyzed contents of billions of URLs and studied 4.5 million pages in-depth to reach the confirmed figure of sites, successfully launching malware binaries and a further 700,000 URLs were identified with similar threat but with a lesser probability.