Hi Jonathan,
Unknown files are reported by Software Signature scan if option "Report unknown Executable Files (Time Consuming)" is checked in the properties of "Software Inventory Configuration" collect task
All .exe files found in the machine which are not associated to a known signature are reportes as unknown files.
In following document you could see the list of currently supported vendors and applications for creation of new Software Signature.
https://support.ca.com/phpdocs/0/5585/5585_Supported_Content.pdf
In this community documents with title like "CA - PROACTIVE NOTIFICATION*" are regularly posted with new patches and new Software Signatures.
Example the last one :
CA - PROACTIVE NOTIFICATION - CACNT - PRODUCT UPDATE - PCACNT-100484
Thanks.
Regards,
Jean-Yves