一Most viruses attack personal computers.More than 10,000 viruses have appeared so far,and unscrupulous programmers generate roughly another six every day.Fortunately,only a handful have been detected far afield .There are three main classes of PC viruses (and the categories for other systems are analogous):file infectors,boot-sector viruses and macro viruses.Roughly 85 percent of all known viruses infect files containing applications such as spreadsheet programs or games.When a user runs an infected application,the virus code executes first and installs itself independently in the computer's memory so that it can copy itself into subsequent applications that the user runs.Once in place,the virus returns control to the infected application;the user remains unaware of its existence.Eventually a tainted program will make its way to another computer via a shared diskette or network,and the infection cycle will begin anew.大多数病毒攻击个人电脑。
超过10,000病毒到目前为止已经出现，无良程序员大致每天产生另外六种病毒。
幸运的是，只有极少数被侦测出是生僻的。
计算机病毒主要有三大类（类似于其他系统的类别）：文件传染，引导扇区病毒和宏病毒。
大约85％的所有已知病毒的感染文件包含的应用程序，如电子表格程序或游戏。
当用户运行受感染的应用程序，病毒代码先执行，并安装在计算机本身独立的内存，因此，它可以复制到随后的应用程序，用户运行。
一旦到位，该病毒将控制返回到受感染的应用程序，用户仍然不知道它的存在。
污点方案最终将通过一个共享的软盘或网络方式到另一台计算机，感染周期将重新开始。
二A company might set up only one or two machines to handle a specific protocol and ban that protocol on all other machines.1)Ports-Any server machine makes its services available to the Internet using numbered ports.For example,if a server machine is running a Web (HTTP)server and FTP server,the Web server would typically be available on port 80,and the FTP server would be available on port 21.A company might block port 21 access on all machines.2)Specific words and phrases ---This can be anything.The firewall will sniff(search through)each packet of information for an exact match of the text listed in the filter.For example ,you could instruct the firewall to block any packet with the word "X-rated"in it .Thekey here is that it has to be an exact match.The "X-rated"filter would not catch "X-rate"(no hyphen).But you can include as many words,phrases and variations of them as you need.公司可能只有一个或两个机器来处理特定的协议，该协议禁止所有其他机器上。
1）端口——任何服务器计算机都使用带编号的端口向互联网提供服务，每个端口对应于该服务器上提供的一项服务。
例如，如果服务器计算机正在运行Web（HTTP）服务器和FTP服务器，则通常可以通过端口80访问Web服务器，并可以通过端口21访问FTP服务器。
除一台计算机外，公司可能阻止对公司内其他所有计算机上的端口21进行访问。
2）特定词汇和短语——这可以是任意内容。
防火墙将嗅探（彻底搜寻）每个信息数据包，确定是否存在与过滤器中列出的文本完全匹配的内容。
例如，您可以指示防火墙阻止任何含有“X-rated”一词的数据包。
这里的关键在于必须是精确匹配。
“X-rated”过滤器不会捕捉“X rated”（不含连字符）。
但您可以根据需要包括任意多的词汇、短语以及它们的变体。
三Public key cryptography----The distinguishing technique used in public key cryptography is the use of asymmetric key algorithms ,where the key used to encrypt a message is not the same as the key used to decrypt it.Each user has a pair of cryptographic keys---a public key and a private key.The private key is kept secret,whilst the public key may be widely distributed.Messages are encrypted with the recipient's public key and can only be decrypted with the corresponding private key.The keys are related mathematically,but the private key cannot be feasibly(i.e. in actual or projected practice)derived from the public key.公钥加密----用于公钥加密识别技术是使用非对称密钥算法，用于加密信息的关键是不能用于解密的密钥相同。
每个用户都拥有一对密钥---一个公共密钥和私人私钥是保密的，而可能广泛分发。
消息与收件人的公共密钥加密，并只能用相应的私人密钥。
键解密涉及数学，但私钥不能切实（即在实际或预计的实践）从公共密钥派生。
四The word "multimedia" has turned into a type of two-edged sword .Although most computer professionals have heard the word, many don't know exactly what it means. This is especially true when the word is applied to everything from talking games to voice-controlled television sets. Essentially,multimedia is the integration of text,audio sound,static graphicimages, animations and full-motion video. Multimedia may use some or all of these aspects of communication.The Windows operating environment gives the user an almost infinite range of expressing text.As a multimedia programmer , you can choose what font to display text in,how big (or small)it should be ,and what color it should be display in. By displaying text in more than one format ,the message that a multimedia application is trying to portray can become more understandable.多媒体一词现在已变成一种“多刃剑”。
虽然大多数计算机专业人员都听说过这个词，但并不确切了解它的含义，尤其是当从声控游戏到声控电视机等任何事情都用多媒体这个词时更加如此。
实质上，多媒体可能部分或全部使用这些交流方式。
Windows操作环境赋予用户几乎无限的范围来表达文本。
作为多媒体程序员，你可以选择要显示文本的字体、大小、颜色等。
通常，用多种形式显示文本可使人们更加容易理解多媒体应用程序试图表达的信息。
五These are in order of decreasing flexibility and increasing simplicity .Enterprise computer means that you purchase hardware and software and hire a staff of developers to create your e-commerce web site .Amazon, Dell and all of the other big players participate in e-commerce at the enterprise lever.Virtual hosting services give you some of the flexibility of enterprise computing ,but what you get depend on the vendor .In general the vendor maintains the equipment and software and sells them in standardized packages .Part of the package includes security ,and almost always a merchant account is also an option .Database access is sometimes a part of the package .You provide the web designers and developers to create and maintain your site.这些方法的目的是降低灵活性，增加简便性。