not able to clean up OSX/Yontoo-B

Do you know where the file was detected?  I'll assume that the Quarantine Manager either doesn't show the full path or the path is blank.

If the full path is not shown you'll have to dig into the log file for the scan that found the item.  See...

http://openforum.sophos.com/t5/Mac-tools-help/Where-are-the-logs-for-SAV-for-Mac/td-p/16091 

If the path is completely blank - even after you have authenticated with the padlock - then just clear the item and rescan your computer.  You may want to exclude Time Machine backups etc. to speed up the scan time.  See:

You are correct ruckus. The path did not show up.

I looked further into digging for the path and - it still doesn't show up. BTW, the link didn't work but I did find the article at 

http://openforum.sophos.com/t5/Mac-tools-help/Where-are-the-logs-for-SAV-for-Mac/m-p/16091/highlight/true#M61

I watched the video and rescanned, excluding my Time Machine Backup. It now says all clear. Does this mean the "threat" is on the Time Machine Backup?

Thank you.

Can't say for sure.  Maybe it was (is), or maybe the item was in a temporary location like a web browser cache that got cleared out.

You could obviously scan the Time Machine volume again - maybe set up a custom scan of just that volume.  That would give a clearer idea.