The patch closes loopholes that together left users of almost every operating system vulnerable to infection by viruses.

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On the other hand, some viruses have caused so much damage that a simple reinstallation of the operating system was insufficient to repair them.

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Rather, Jackson found, it slowed down the operating system, increased the likelihood of a crash and made it easier for "malicious viruses" to find their way from the Internet onto our computers.

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Most viruses and other malware are designed for Windows, because that's the most popular operating system.

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