+1 to Camerons advice.
Additionally myself I have multiple external drives and my most critical data go through a drive rotation where I have my external drives labelled and so of the 5 external drives I have I constantly backup in the order of 1,2,3,4,5,1,2,3,4,5.... so that I have 4 prior backups before the recent backup. Anything that is extremely critical to not have overwritten or deleted I burn to DVD-R disc to place it in a read-only state. Every time an external drive is connected that allows read/write you have the risk that if your system has a virus on it that it can target the data on the external drive when connected.
About 20 years ago I lost a large amount of data from a virus that destroyed my data. The only data that I had that was safe was what was burn to CD-R's. I had floppies that were infected and i wasnt running an antivirus. I use to download all sorts of free and shareware software back then and one of them had a trojan that spread like fire through floppy disks. I had 5 computers infected because I thought the floppy disk was having a read problem in one computer so I put it into another, and then another system, and then was trying to use tools to gain access to my data on that floppy again not knowing that a virus was on it and mangled the data on it. I had a small fire of a problem that spread into a bigger fire of a problem because I didnt think that a virus would act like this. Each system that the floppy was placed into and disk accessed got infected. When I finally realized the problem I had I realized that I didnt have safe backups of the larger amount of my data. I put trust into having 2 systems with their hard drives storing the large amount of data and 2 systems wouldnt fail at the same time. Well this thought cost me a ton of lost data back then as for I only thought of a drive failing that 2 systems drives wouldnt fail at the same time, however both got infected at the same time, and after cleaning out the virus infection, trying to access my data after was a mess of corruption that I sadly had to just format the drives and start clean and take that loss of so much stuff I had that I created myself or downloaded off the internet through hours and hours of dialup downloads all gone.
