The legality of making backups of software you have bought hasn't been fully tested in court, and will also depend upon where you live.
In the U.S. it was a protected right. It's section 117 of the Copyright law. The original intent was to ensure a viable copy of software that came on volatile media, namely floppy disks. It was tested several times that I can recall, one of the cases involving Nintendo. Every time new media is introduced (floppy disks, solid state, CD, DVD) the law gets tested in court.
It's the DMCA that hasn't been properly contested in court. Combined with the HSA, it complicates a lot of things for the average joe and makes for a legal nightmare for everyone.