A computer virus is a program or piece of code that is loaded onto your computer without your knowledge and runs against your wishes . All computer viruses are man-made . Here are some virus prevention tips :
Do not open any files attached to an e-mail from an unknown , suspicious or untrustworthy source .
Do not open any files attached to an e-mail unless you know what it is ,even if it appears to come from a dear friend or someone you know . Some viruses can replicate themselves and spread through e-mail Better be safe than sorry and confirm that they really sent it .
Do not open any files attached to an e-mail if the subject line is questionable or unexpected. If the need to do so is there always save the file to your hard drive before doing so.
Delete chain e-mails and junk e-mail . Do not forward or reply to any of them . These types of e-mail are considered spam ,which contains lots of annoying advertisements and useless information.
Do not download any files from strangers .
Be careful when downloading files from the Internet . Ensure that the source is a legitimate and reputable one . Verify that an anti-virus program checks the files on the download site . If you’re uncertain, don’t download the file at all or downloaded the file to a floppy and test it with your own anti-virus software.
Update your anti-virus software regularly . Over 500 viruses are discovered each month, so you’ll want to be protected. These updates should be at least the products virus signature files . You may also need to update the product’s scanning engine as well .
Back up (备份)your files on a regular basis . If a virus destroys your files ,at least you can replace them with your backup copy. You should store your backup copy in a separate location from work files , one that is preferably not on your computer.

计算机病毒是一种程序，或者说是一段代码，它往往是偷偷地侵入你的电脑，任意发作。 所有电脑病毒都是人为的。这里是一些防备病毒的小贴示：

对那些你不熟悉的、可疑的、或者是不确认的电子邮件附件，不要打开。
不要打开那些标题不自然、或者不了解的电子邮件。如果必须打开，先把文件存入硬盘。
删除邮件链接和垃圾邮件，更不要点击进入。这种邮件会带有恶意连接，带来大量的讨厌广告和没用的信息。
不要从陌生地址下载文件。
从网络上下载文件都要小心，要确认其来源是合法的、供应商是有信誉的。用杀毒软件检查下载页面的文件。如果你不确定，就干脆不要下载。你也可以先把文件下载到一张软盘上，再用自己的杀毒软件检查。
定期升级你的杀毒软件。每个月都会发现500个以上的病毒，所以你要保护自己。这些升级应该含盖出现的病毒列表。你也须要升级杀毒软件的扫描器。
经常备份你的文件。如果有病毒入侵毁坏你的文件，你起码可以恢复文件内容。你应该把备份的文件放在不同的区域，最好不在一台相同的电脑。