When trading via your computer, you generally connect to your broker via the Internet. And if you connect to the Internet, you open your computer to the outside world. By doing this you expose your computer to computer viruses. The way to combat that threat is to install antivirus software on your computer. Antivirus software is designed to scan and monitor your computer for computer viruses and other malicious software called malware. If it identifies a computer virus or malware, it then either quarantines or removes that rogue software so that it won't harm your computer. Most good antivirus programs also scan your email for viruses.
One of the problems of antivirus software is that it is generally a resource hog. Although it slows down performance, it is essential that you always have the antivirus software running in the background. A way to overcome the slow down in performance is to buy a more powerful computer. Using antivirus software is another form of insurance that is required if you want to be a successful trader.