Benjamin Daines was browsing the Web when he clicked on a series of links that promised pictures of an unreleased update to his computer's operating system. Instead, a window opened on the screen and strange commands ran as if the machine was under the control of someone -- or something -- else. Daines was the victim of a computer virus. Such headaches are hardly unusual on PCs running Microsoft's Windows operating system. Daines, however, was using a Mac -- an Apple Computer machine often touted as being immune to such risks.

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