The computer virus is an outcome of the computer overgrowth in  the 1980s．The  cause  of  the  term "computer  virus" is the likeness between the biological virus and the evil program infected with computers．The origin of this term came from an American science fiction“ The  Adolescence of P－1“　written  by Thomas J. Ryan，published in 1977．Human viruses invade a living cell and turn it into a factory for manufacturing viruses. However, computer virusesare small programs. They replicate by attaching a copy of themselves to another program.

   Once attached to me host Program，the viruses then look for other programs to "infect"．In this way， he virus can spread quickly throughout a hard disk or an entire organization when it infects a LAN or a multi-user system． At some point，determined by how the virus was programmed the virus attacks．The timing of the attack can be linked to a number of situations，including a certain time or date， the presence of a particular file，the security privilege level of the user，and the number of times a file is used．Likewise，the  mode  of  attack varies．So－called "benign"  viruses might simply display a message，like the one that infected IBM’s main computer system last Christmas with a season's greeting．Malignant  viruses  are  designed to damage the system．The attack is to wipe out data， to delete flies， or to format the hard disk.

What Kind of Viruses Are There？

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

    Shell viruses wrap themselves around a host program and don't modify the original program．Shell programs are easy to write，which is why about half of viruses are of this type．

    Intrusive viruses Invade an existing program and actually insert a portion of themselves into the host program．Intrusive viruses are hard to write and very difficult to remove without damaging the host file.

    Shell and intrusive viruses most commonly attack executable program flies－those with a．corn or．exe extension， although data flies are also at some risk．

    Operating system viruses work by replacing parts of the operating system with their own logic．It is very difficult to write operating system viruses and these viruses have the ability once booted up， to take total control of your System．FOF example，some operating system viruses have hidden large amounts of attack logic in falsely marked bad disk sectors．

    Source code viruses are intrusive programs and they are also inserted into a source program such as those written in Pascal prior to the program being complied．There are the least－common viruses because they are not only hard to write，but also have a limited number of hosts compared to the other types．

Be Wary of the Second Network Viruses

    Do you believe it？ Network viruses can steal money！So far Internet has become the main channel through which the computer viruses spread．Look，here come the second network computer viruses．Even without "snatching" information from  the network your computer can be infected by the second network computer viruses， which are hidden in some machines on the network． Your computer is， so to speak， in danger once being connected to the network to browse．

    The virus that can steal your money belongs to a kind of the second network viruses.  It was designed and put in some machines on the network． When your computer is linked to one of these machines，the virus will invade your hard disk and search whether Intuit Quicken， an accounting software， is installed． One of this accounting software's functions is to transfer accounts automatically. Once infected， your money will be transferred to an additional account opened by the virus program without anybody knowing it．

計(jì)算機(jī)病毒

    計(jì)算機(jī)病毒是八十年代計(jì)算機(jī)飛速發(fā)展帶來(lái)的結(jié)果，計(jì)算機(jī)病毒這一名詞起因于在計(jì)算機(jī)上傳染的有害程序與生物學(xué)中病毒的相似性，該名詞起源于1977年出版的、由 Thomas J． Ryan寫(xiě)的一本美國(guó)科幻小說(shuō)《p-1的青春》。人體病毒入侵活的細(xì)胞后，就把它轉(zhuǎn)變成制造病毒的工廠。而計(jì)算機(jī)病毒是一些小程序，它們把自己的一個(gè)副本附加到另一個(gè)程序上面進(jìn)行復(fù)制。

    病毒程序一旦附加到一個(gè)主程序上，就開(kāi)始尋找其他可以進(jìn)行“感染”的程序。這樣，病毒就很快地布滿整個(gè)硬盤(pán)，如果病毒感染了一個(gè)局域網(wǎng)或者一個(gè)多用戶系統(tǒng)，那么就在整個(gè)組織內(nèi)進(jìn)行擴(kuò)散。只有在某個(gè)點(diǎn)上病毒程序才會(huì)發(fā)作（這是由病毒程序的設(shè)計(jì)所決定的）。攻擊的時(shí)間與多種情況有關(guān)，包括：某個(gè)時(shí)間或日期、特定用戶識(shí)別符的出現(xiàn)、用戶的安全保密等級(jí)和一個(gè)文件使用的次數(shù)。同樣，攻擊的方式也是各種各樣的。所謂的“良性”病毒可能只是簡(jiǎn)單地顯示一個(gè)消息，如在去年圣誕節(jié)時(shí)，受感染的IBM公司的主要計(jì)算機(jī)系統(tǒng)顯示節(jié)日問(wèn)候。惡性病毒被設(shè)計(jì)出來(lái)破壞系統(tǒng)。常見(jiàn)的攻擊方式是消除數(shù)據(jù)、刪除文件或者格式化硬盤(pán)。

病毒程序有哪幾種？

    有四種類(lèi)型的病毒程序：外殼型、入侵型、操作系統(tǒng)型和源碼型。

    外殼型病毒將它們自己包裹在主程序的四周，對(duì)源程序不作修改。外殼型病毒容易編寫(xiě)，這也正是約有一半病毒程序是這種類(lèi)型的原因。

    入侵型病毒侵入已有的程序，實(shí)際上是把病毒程序的一部分插入到主程序中。入侵型病毒難以編寫(xiě)，在去除它們時(shí)常常會(huì)破壞主文件。

    外殼型和入侵型病毒通常攻擊可執(zhí)行文件，即帶有.COM或．EXE擴(kuò)展名的文件。當(dāng)然數(shù)據(jù)文件也有受攻擊的危險(xiǎn)。

    操作系統(tǒng)型病毒發(fā)作時(shí)用自己的邏輯代替部分操作系統(tǒng)。這些病毒程序的編寫(xiě)非常困難，它們一旦得手就有能力控制整個(gè)系統(tǒng)。例如，一些操作系統(tǒng)型病毒把自身的邏輯隱藏在那些標(biāo)識(shí)“壞”的磁盤(pán)扇區(qū)中。

  源碼型病毒是入侵程序，它們?cè)诔绦虮痪幾g之前插入到諸如用PASCAL編寫(xiě)的源程序中，它們是最少見(jiàn)的病毒程序，因?yàn)樗鼈儾粌H編寫(xiě)困難，而且與其他類(lèi)型的病毒相比，受它們破壞的主程序數(shù)目也有限。

小心第二代網(wǎng)絡(luò)病毒

    相信嗎？網(wǎng)絡(luò)病毒會(huì)偷錢(qián)！ 目前，因特網(wǎng)已成為電腦病毒傳播的主要渠道。瞧，第二代網(wǎng)絡(luò)病毒又來(lái)了。無(wú)需從網(wǎng)上“抓取”資料，你的機(jī)器就會(huì)感染上第二代網(wǎng)絡(luò)病毒，這種病毒匿藏于網(wǎng)絡(luò)上的一些機(jī)器中。一旦連接上網(wǎng)測(cè)覽，你的機(jī)器就可以說(shuō)是處于危險(xiǎn)之中了。

    會(huì)偷錢(qián)的病毒屬第二代網(wǎng)絡(luò)病毒。這種病毒被設(shè)計(jì)出來(lái)之后，就放置在網(wǎng)上的一些機(jī)器中。當(dāng)你的計(jì)算機(jī)連接到這樣的機(jī)器上時(shí)，病毒就會(huì)入侵到其硬盤(pán)內(nèi)，并搜尋其中是否裝有“Intuit Quicken”理財(cái)軟件。此理財(cái)軟件的功能之一就是自動(dòng)轉(zhuǎn)帳。一旦感染第二代病毒，你的錢(qián)就會(huì)神不知鬼不覺(jué)地被病毒程序轉(zhuǎn)到它所建立的其他帳戶上了。