Ransomware writers are aware that backups are an effective defense and are modifying their malware to track down and eliminate the backups. SamSam and Ryuk are two well-known examples of ransomware that have backups in its sights. The more barriers there are between an infected system and its backups, the harder it will be for the ransomware to get to it. The most common way of doing this is through a Microsoft Windows feature called Previous Versions, which allows users to restore earlier versions of files.”]
Source: https://www.csoonline.com/article/3331981/how-to-protect-backups-from-ransomware.html