It seems that BitDefender for Mac automatically scans all new files, including those on external HDDs. Whenever I plug in an external HDD, BitDefender starts scanning files on the external HDD (as shown by its icon at task bar). I cannot "safely eject" the external HDD until BitDefender stops scanning, which may well take hours.
This generates quite some inconvenience. I am using my HDD just to copy a few files, yet I have to wait few hours before I can remove the HDD. I have not tried handling DVDs on my Mac, but given the slow speed of DVDs, I expect a nightmare...
I suggest that BitDefender should not automatically scan external HDDs/drives. Or at least, users should be allowed to opt-out.
Thank you very much 
PS: I know that I can add exclusions. But then I have to create exclusions for each of my drives, which would still be quite inconvenient.
PS: This problem occurs once per external HDD. The second time I use the same HDD, there are no new files to scan.