Internet, Networking, & Security Antivirus Frequently Asked Questions About Antivirus Software by Mary Landesman Writer Mary Landesman is a former freelance contributor to Lifewire and a security expert. She was named as one of the women to watch in IT security. our editorial process LinkedIn Mary Landesman Updated on July 21, 2019 Koron / Getty Images Antivirus Online Scams Social Media Scams Email Scams Phone & Texting Scams Tweet Share Email The best antivirus software is the one that works best on your system, has the features you want, and is easy for you to use. Because every system is unique, if you're shopping for new antivirus software, you should evaluate several products to find the one best suited for your PC and your level of experience. Of course, you'll want to stick with only qualified, reputable antivirus products that have received certification from the three major certification authorities: Checkmark, ICSALabs, and VB100 and which have performed well on the rigorous tests conducted by AV-Test.org. There is also the question of paid or free antivirus. While generally speaking, the paid antivirus offers more features that can provide complete protection, those building an a la carte security solution may fare better with one of the free standalone antivirus scanners. For specific recommendations on best of class in their respective categories, see the following: Do You Need Both an Antivirus and an Anti-Spyware Scanner? It depends. Some antivirus products, notably McAfee VirusScan, include stellar spyware protection, but many others do not. If you are experiencing ongoing problems with spyware, you might want to consider adding a dedicated spyware scanner to the mix. Do We Have to Uninstall Existing Antivirus Program Before Installing a New One? If you are changing to a new antivirus product, you will need to uninstall the previous antivirus scanner first. After uninstalling, you must reboot your PC before installing the new scanner. If you are simply upgrading the existing antivirus software to a newer version of the same product, there is no need to uninstall the older version first. However, if the new version is two or more versions newer than the old, then you will want to uninstall the old version before installing the new. Again, anytime you uninstall an existing antivirus product, be sure to reboot the computer before installing the new scanner. Can Two Antivirus Scanners Be Run on the Same System at the Same Time? In the past, It was never a good idea to run two antivirus scanners simultaneously. However, if only one of the scanners has real-time protection enabled and the second scanner is used only to manually scan selected files, they may possible co-exist peacefully. Some Software is designed to be the 2nd scanner on a system. In a few cases, an antivirus scanner will not install if it detects another antivirus scanner already installed on the system. Why Does One Scanner Detect a Virus When Another Does Not? Antivirus is largely signature-based. The signatures are created by the individual vendors and are unique to their products (or the products that use those particular scanning engines. Hence one vendor may have added detection (i.e. a signature) for a particular malware while another vendor may not have. For this reason, it is oftentimes better to run two different anti-virus applications.