the license says "LIMITED USE LICENSE
Subject to the terms and conditions of this License and to Ancestry.com's receipt of any applicable payment, Ancestry.com grants to you the non-exclusive right to install and operate two (2) copies of the Product on computers within the same household only for personal, noncommercial purposes. This License, and the restrictions set forth herein, applies to the Software and the Content."
I installed it on two machine with the FTM files on a network share. We just use it one at a time. My files are backed up in two external locations, one an eSATA drive and the other A Western Digital DX4000 network backup machine. It runs Microsoft Windows Storage Server 2008 R2 Essentials software and will backup 25 machines.