i see no problem purchasing the 2016 for download through www.quicken.com
if that link does not work what i did was go to http://www.quicken.com/compare
click on the blue buy box in the deluxe section
you should notice in the check out section a drop down box called "delivery method"
which can be switched between download and cd
as for preventing corruption
i recommend doing a clean install using the utilities and instructions on this page to remove all traces of older installs
also you want to keep the data file on the c drive and not on a network drive or cloud drive
you want to run validation on it every once in a while to make sure it is not corrupted
file / file operations / validate and rebuild
and most importantly you want to make backups every day and keep about a weeks worth and maybe 1 for each month beyond that week. While many people use quicken for years with no problem, corruption does happen and the fixes are limited to the validation routine. Having a good backup at all times is essential.