I am trying to install 1.6.8 on a Mac.
I have downloaded the file several times and each time when I try to open the system says the file is damaged and must be trashed.
In searching the forum it appears that the checksum maybe incorrect and needs to be fixed on the developer end.
Is my experience unique?
I am currently using 1.6.8 on Mac OS X 10.11.4
A bunch of people have had IDE 1.6.x problems, including IDE crashes and bizarre compile errors, when they had a previous 1.5.x/1.6.x installation. At least some of those problems seem to be caused by out-of-date executables that the IDE saves outside the IDE installation directory. Perhaps that is what is causing your particular problem. In such cases it appears that the fix is to delete or rename the old "Arduino15" directory and re-install 1.6.x.
On Mac OS X:
/home/(username)/.arduino15 (a.k.a. ~/.arduino15)