A computer virus is a program or piece of code that is loaded onto your computer without your knowl- edge and runs against your wishes. All computer viruses are manmade. 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(復(fù)制) themselves and spread through e- mail. Better be safe that 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(轉(zhuǎn)寄) or reply to any of them.These types of e-mail are considered spam(垃圾郵件)， 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(合法的) and reputable one. Verify(證實(shí)) that an anti-virus program checks the files on the download site. IT you are uncertain， don't download the file at all or download the file to a floppy(軟盤) 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 up- date the product's scanning engine as well.

　　Back up(備份) your files on a regular basis. IT 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 your work files，one that is preferably not on your computer.

　　44.This passage mainly tells us .

　　A. what a computer virus is B. how to use e-mail safely

　　C. how to use computers safely D. how to prevent computer viruses

　　45.Which of the following statements about computer virus is TRUE?

　　A. A computer virus is a kind of worm

　　B. Not all computer viruses are manmade

　　C. Computer viruses run according to our wishes

　　D. A computer virus is a program or piece of code

　　46.When we use e-mail，we should .

　　A. open all the files we receive

　　B. open any file even if we don't know what it is

　　C. not open any files if the subject line is questionable

　　D. forward or reply to junk e-mail.

　　47.Which of the following statements is NOT true?

　　A. We'd better not download any files from strangers.

　　B. We'd better download files from a legitimate and reputable source.

　　C. We should update our anti-virus software regularly.

　　D. We should store our backup copy in the same location as our work files.