/mnt/HDA_ROOT
/share/CACHEDEV1_DATA/.qpkg/MalwareRemover/
みましたが見当たらず。

参考になるかわかりませんがそれっぽいログを
警告 2021-04-23 03:02:20 admin 127.0.0.1 Malware Remover Malware Removal [Malware Remover] Removed high-risk malware. Immediately update QTS and all applications to their latest versions and use stronger account passwords. Weak passwords make the system vulnerable to exploits and malware.
警告 2021-04-23 03:02:23 admin 127.0.0.1 Malware Remover Malware Removal [Malware Remover] Removed malware. You must restart the NAS.
警告 2021-04-23 03:02:24 admin 127.0.0.1 Malware Remover Malware Removal [Malware Remover] Removed the detected malware: MR2102
情報 2021-04-23 03:02:24 admin 127.0.0.1 Malware Remover General [Malware Remover] Scan completed.
情報 2021-04-24 00:33:28 admin 127.0.0.1 App Center App Installation [App Center] Installed Malware Remover4.6.1.1 in "/share/CACHEDEV1_DATA/.qpkg/MalwareRemover".