This is one question that people often ask. A slow computer will decrease productivity, so increasing the time needed for a work to be done. There are few reasons why your computer becomes slow and one of it is malicious software. Below are some of the malicious software that can cause you the problem.
Adware is software that displays advertising and consumes your bandwidth. If you're a broadband user, you will not feel the effect. But if you're on dial-up, you can feel that it's sucking your bandwidth. However, even if you're using broadband, but you have lots of this malware software inside your PC, it can also cause your computer to become slow.
Spyware is software that gathers sensitive information from your computer such as username and password. This activity happens in the background and will increase your CPU usage and your computer will not be running smoothly.
Key logger is also one of the malicious software that causes a slow computer. Just like the spyware, keylogger records every of your keyboard strokes and send it to its creator. It consumes CPU usage and your bandwidth.
4. Computer Worm
A computer worm is malicious software that can infect a computer and send copies of itself to another computer in the network. This causes the infected computer to become a zombie computer and can be controlled by the worm creator. The zombie computer then will use to perform DDoS attack to another host.
Usually these are the reasons why your computer becomes slow and what you need to do is learn how to remove it. However, removing all of these malicious software is just half the battle, what you need to know is how to prevent you from being infected again.