Windows malware found in Mac OS X files

Hello,

Sophos for Mac has found several pieces of Windows malware on my system.  This is typically not a huge surprise but what is torublesome this time is that the files shown to contain the malware are Mac specific files - things like PLIST files, etc.

Is this correct?  If not, is this a false positive and just a hiccup with the Sophos AV system?

Thanks in advance for your help.