Download of spyware, a computer virus or any kind of malware that happens without knowledge of the user. Drive-by downloads may happen by visiting a website, viewing an e-mail message or by clicking on a deceptive popup window: the user clicks on the window in the mistaken belief that, for instance, it is an error report from his own PC or that it is an innocuous advertisement popup; in such cases, the “supplier” may claim that the user “consented” to the download though he was completely unaware of having initiated a malicious software download