Do you find that when you are busy with your study on the Internet, the speed of your computer slows down     sometimes? It is probably because your computer gets infected by virus (病毒), which can make it more difficult for you to use the computer. How to keep viruses your computer is a problem now. But in fact, nothing can ensure (保证) the security of your computer one hundred percent. There are, somehow some things you can do to   your computer’s security system and decrease (降低) the possibility of an infection.
You can    your system up to date with the current anti-virus software (反病毒软件), and use the following methods