I googled the installer integrity check failed message, literally the first 5 words...and thank you google, first link was this.
If this still doesn't work, then idk, but next time, try googling, or even using the search function here.
Since this happens at install, then it wasn't Shaggy, but something else.
Clear your browser's cache.
FailedDisable any download accelerators or managers and download the installer again.
FailedRename the installer so it is a simple one-word name with no special characters (without removing the .exe suffix)
FailedDownload the installer from another source approved by the software developer or publisher.
FailedIt might be corrupted on the server, or the connection to the server is unreliable from your location.
PendingUpdate your anti-virus software (if installed) and download the installer again.
N/ADisable your anti-virus software and download the installer again.
N/ADownload the installer using another computer and copy it to the original computer.
PendingIf you have the nVidia firewall installed, uninstall the program and download the installer again.
N/AScan for, and remove malware and viruses on your system.
FailedScan the hard drive using scandisk, chkdsk, or any other hard drive repair tool.
FailedFor people of ROMANIA who use FireFox in Romanian language try this tutorial:
http://www.tutorialepc.ro/nsis-error-error-launching-installer-remediere-problema-2.html N/AWait for Windows Update to finish updating drivers.
N/AFailed being the methods I tried and failed, N/A being an unavailable method due to program(s) already been removed, never installed to begin with, or already done, and Pending being methods not yet confirmed for success or failure.