Dear Mr.Verma,
As per your query, the fbackup feature of eScan is basically used to keep an encrypted backup of the important system files on your machine.
The mentioned feature has been implemented primarily for a scenario wherein a system might get infected by a new variant of a file infector virus like sality.In such cases, if the disinfection of a file is not possible,the file will be replaced with the copy in the fbackup folder.
For more details about the mentioned feature and settings info,please refer the below link
http://wiki.escanav.com/wiki/index.php/Escan/english/eScan-FAQ119