Answer lies in the read me file that should have come with the software. But reproduced for your convenience below
In some situations, Fast & Safe Cleanup may report space can be freed even after pressing the Clean Now button. This is due to Windows preventing Fast & Safe from deleting certain files. This is harmless and can be ignored
If u r the subject of back door trojans then u should invest in a good firewall. But this must be properly configured to ensure all unused port or configured correctly
Hope info help. Happy surfing