If warning of
    "<file name> is not commonly downloaded
     and could be dangerous"
is given by the downloading of the file, ....


The browser gives the warning such as follows for the file which was uploaded recently.
In that case, please choose [ Keep ] in defiance of warning.

---- Chrome ----
      "<file name> is not commonly downloaded and could be dangerous"
---- Internet Explorer ----
      "This program is not commonly downloaded and could harm your computer"

     


Even if the file does not have a problem at all, this warning is given.

This warning is given for a file with a little number of the downloading
from the statistics data which a browser collects.

In other words, it becomes targeted for warning for a reason "uploaded recently"
even if a file does not have a problem.