The definition files contain signatures for viruses and other malware that have been encountered in the wild. That’s why it automatically downloads new, updated definition files – once a day or even more often. Your antivirus software relies on virus definitions to detect malware. However, you don’t usually have to run full system scans yourself when an antivirus program is already protecting you – it’s always scanning in the background and doing its own, regular, full-system scans. If you want to repair an already-infected computer, inserting its hard drive in another computer and performing a full-system scan for viruses (if not doing a complete reinstall of Windows) is useful. These full disk scans can also be helpful when repairing a computer. This ensures that the latest virus definition files are used to scan your system for dormant viruses.

Most antivirus programs set up scheduled full system scans, often once a week. A full system scan is helpful when you’ve just installed an antivirus program – it ensures there are no viruses lying dormant on your computer. If you download a virus to your computer, your antivirus program will notice immediately – you don’t have to manually initiate a scan first.įull-system scans can be useful for some things, however. (It’s also hard to be sure that the malware has ever been completely removed.)īecause of the on-access scanning, it isn’t usually necessary to run full-system scans. After a virus has infected your system, it’s much harder to remove. It’s possible to use an antivirus without on-access scanning, but this generally isn’t a good idea – viruses that exploit security holes in programs wouldn’t be caught by the scanner.

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