Before running through these steps you should clear the virus alert from your quarantine via Sophos Endpoint Security and Control. To clear the Shadow volume copy:
Once the system has rebooted then please run a full system scan to check for the infection. When the system has been confirmed clean then the disabled shadow copy can be re-enabled.
On occasions the detection exists but the Windows shadow copies are not enabled. You should check for any non-Microsoft backup utilities for example 'Backup Exec'. When using third party backup software then you should contact the software vendor for instructions purging the restore.
If no third party application is used you can try enabling the backups to create a restore point and then proceed with the above steps to purge the shadow copy.
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