Users who clicked on the links became vulnerable to programs installed on their computers that were designed to steal bank codes, send spam and engage in click fraud.

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Along with millions of other out-of-date and unsecured PCs strung together by the Internet--what Corman calls "the leper colony"--those machines represent a combined mass of computing power responsible for most of the Net's spam e-mails, much of its click fraud, and the vicious "denial of service" attacks that can knock sites offline and even destroy online businesses altogether.

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This classification is typically in the form of requesters asking you to sign up for services, register for events, click to sites, send email or notifications to others, and other actions to pad numbers of registrations or directly spam information.

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