According to a computer virus intrusion system approach can be divided into source virus, computer virus virus, operating system viruses and shell viruses.

按计算机病毒入侵系统的途径可将计算机病毒分为源码病毒、入侵病毒、操作系统病毒和外壳病毒。

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There are four main types of viruses: shell, intrusive, operating system and source ode.

有四种类型的病毒程序：外壳型、入侵型、操作系统型和源码型。

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There are four main types of viruses: shell, intrusive, operating system and source ode．

有四种类型的病毒程序：外壳型、入侵型、操作系统型和源码型。

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

BBC: Oracle issues patch for Java loopholes

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

CNN: Technology - Analysis: Understanding viruses

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.

CNN: ASIANOW - TIME Asia | Cover: 'Microsoft Enjoys Monopoly Power...'