I'll appreaciate all of your response here. This is the scenario, I have an external hd with a total capacity of 232.76 GB I have old backed up files already in there from 2 years ago (my last backup after a big crash an loss of data) I have 75.65gb remaining on the external and 40Gb remaining on my internal HD. I have some corrupt files and want to do a back up before I run a anti-virus program. I don't know which back-up to choose. I'm afraid to do the erase back up. Because there may be stuff in there from my former computer, I don't know. I don't know if the smart update is enough or if the newer or different file options are too much. My space is limited. What do I choose if I don't want to double up on any of the old info and don't want to loose any of the old info? Do you think I am being overly cautious? Please help, I am computer illiterate for the most part.