I know that a lot of folks are reluctant and perhaps suspicious of cloud apps and especially using the “cloud” as a back up. The “cloud” is just a convenient way of referring to online storage and access of files and programs not on your specific computer, tablet or even phone. As far as I know, most if not all cloud applications are relatively secure, but even if you don’t trust this, you can at least back up some important but not sensitive material and then back up the really sensitive stuff to some other destination such as an external hard drive or flash drive.
At any rate, I think that the cloud is a great thing, and especially for keeping current back ups. I use several free cloud backup sites to store copies of all my important stuff, and have been doing so for several years now.
I have a free Dropbox account that gives, as I recall, 4 gig of free space. (I think I had to do some things to get that much, as they start you out with 2 gig of free space). Dropbox was the first I used and actually quite simple. It is the main service I keep live on my computer to back up my core files automatically. My main problem with it is that you have to put everything into one Dropbox folder and cannot just pick folders off your drive to back up automatically. It is possible that they may have changed this, but if so I am unaware of it.
In addition to Dropbox, I use a Google Drive, which gives me 5 gig free. It is pretty easy and I use it as a second back up of the same stuff on the Dropbox. I don’t want it in the background, though, because it seems to slow things down. I just periodically back up.
I also have a Microsoft SkyDrive with 25 gig free. Yes, 25 gig! But don’t expect to get 25 gig free anymore. I got in on this early on, and now they have massively dropped the free space for new users, but you still get 7 gig free. This service is a bit more of a pain, and really slows things down when it is running, so I do not leave it live on the system, but back up periodically. Since it is such a big drive (and I don’t back up movies), it can hold all my important stuff.
Now finally, I just learned of Bitcasa from an article on Makeuseof. It offers 10 gig free and will backup or mirror folders you specify (unlike Dropbox). In my short experience with it, it is simpler than even Dropbox, and it seems to do the back up quickly. The backup files are encrypted, but I do not know with what method and I cannot guarantee the security. My only complaint is that it seems to really clobber up the system while it is running. It slows things down so much I that do not want it to run in the background, and use it to back up a bunch of PDF books and various downloads. I have been using it only for a few days now, but so far I like it. Especially for free.
But nothing in life is absolutely secure. Websites can go down or go out of business. So I also back things up to flash drives…. just not every single day.
Anyway, I back up just the stuff that I download or create myself (documents, photos, MP3 files, PDF books and lost of portable programs). I do not back up my entire disk, operating system or installed program files. If you do not currently use a cloud back up, one of these may be a good choice for free.