A new knowledge base article explains how to back up the data of PRTG Network Monitor. Most important are the folder "Monitoring Database" and the file "PRTG Configuration.dat", the other files and folders can be left out of your backup-process. Please see the new knowledgebase article How do I backup all data and configuration of my PRTG installation? for a documentation of the various other files and folders - and then choose the data that you want to back up.