I can recommend a program called Handbrake. It's available for Windows, Linux and Mac, but you need to find a version BEFORE 0.9.2 for full decryption as the LIBDVDCSS libraries were removed from then onwards. I haven't tried it myself, but if you can't find an older version then installing VLC media player may restore functions as it includes LIBDVDCSS.
Edited to add, this should only be used for legit backing-up purposes of course...