Windows Security “Opening these files might be harmful...”

Thought this might be of a curious interest - worth a quick post...

I have two mappings to a share, one is mapped using the FQDN, the other mapped using just the HOSTNAME.

C:\Users\labrat>net use X: \\NASVM1-LOADBALANCER.lab.priv\testshare01
C:\Users\labrat>net use Y: \\NASVM1-LOADBALANCER\testshare01

I’ve got a few files in this share. Two of these files - a new ‘Briefcase’ and a new ‘Compressed (zipped) Folder’ exhibit an interesting behaviour.

In the share mapped using the FQDN, trying to open these files gives the:

Windows Security
Opening these files might be harmful to your computer

In the share mapped with the HOSTNAME, we don’t get any warning.

Image: FQDN mapped share and Windows Security warning
Image: HOSTNAME mapped share and no Windows Security warning

A fix is easy and covered in so many other forums and posts, so I’ll sign off for (April) now.



  1. For example, covered in this post:


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