Threat: 'Troj/DocDl-BBK' detected

I received an alert that Threat: 'Troj/DocDl-BBK' was detected, I clicked on the quarantine manager and there was nothing in there, I checked the log and it said:

com.sophos.intercheck: 2016-02-13 08:02:56 -0500 Threat: 'Troj/DocDl-BBK' detected in
com.sophos.intercheck: Access to the file denied

I did a search on the threat and it says it's windows-based threat???

Questions:

Why if its a windows-based thereat, did i get it?

Why wasn't it in the Quarantine Manager after it alerted me?

Why was access denied?

Thanks

Mark