Not all viruses that find their way onto your computer dramatically crash your machine. Instead, there are viruses that can run in the background without you even realizing it. As they creep around, they make messes, steal, and much worse. Malware today spies on your every move. It sees the websites you visit, and the usernames and passwords you type in. If you login to online banking, a criminal can watch what you do and after you log off and go to bed, he can log right back and start transferring money out of your account. Here are some signs that your device might already be infected with malware: Programs shut down or start up automatically Windows suddenly shuts down without prompting Programs won’t start when you want them to The hard drive is constantly working Your machine is working slower than usual Messages appear spontaneously Instead of flickering, your external modem light is constantly lit Your mouse pointer moves by itself Applications are running that are unfamiliar Your identity gets stolen If you notice any of these, first, don’t panic. It’s not 100% that you have a virus. However, you should check things out. Make sure your antivirus program is scanning your computer regularly and set to automatically download software updates. This is one of the best lines of defense you have against malware. Though we won’t ever eliminate malware, as it is always being created and evolving, by using antivirus software and other layers of protection, you can be one step ahead. Here are some tips: Run an automatic antivirus scan of your computer every day. You can choose the quick scan option for this. However, each week, run a deep scan of your system. You can run them manually, or you can schedule them. Even if you have purchased the best antivirus software on the market, if you aren’t updating it, you are not protected. Don’t click on any attachment in an email, even if you think you know who it is from. Instead, before you open it, confirm that the application was sent by who you think sent it, and scan it with your antivirus program. Do not click on any link seen in an email, unless it is from someone who often sends them. Even then, be on alert as hackers are quite skilled at making fake emails look remarkably real. If you question it, make sure to open a new email and ask the person. Don’t just reply to the one you are questioning. Also, never click on any link that is supposedly from your bank, the IRS, a retailer, etc. These are often fake. If your bank sends e-statements, ignore the links and login directly to the banks website using either a password manager or your bookmarks. Set your email software to “display text only.” This way, you are alerted before graphics or links load. When a device ends up being infected, it’s either because of hardware or software vulnerabilities. And while there are virus removal tools to clean up any infections, there still may be breadcrumbs of infection that can creep back in. It’s generally a good idea to reinstall the devices operating system to completely clear out the infection and remove any residual malware . As an added bonus, a reinstall will remove bloatware and speed up your devices too. Robert Siciliano is a Security and Identity Theft Expert. He is the founder of Safr.me a cybersecurity speaking and consulting firm based in Massachussets. See him discussing internet and wireless security on Good Morning America .