Microsoft recommends updating Windows Defender definitions regularly to ensure that the latest available security protection is applied. The frequency of updates depends on how often malware and other threats are released, as well as how quickly they are discovered. Generally speaking, daily updates are recommended. On a corporate system, administrators may choose to set up automated scheduling so that updates occur more frequently. It is important that any operating system, including Windows Defender, is always kept up to date with the latest virus definitions, patches and hotfixes for optimal security.