I don't know how reliable an online service would be, sounds like an excuse for some hacker to get access to your computer and GIVE you viruses to me, but an external hard drive really is your best bet. It's what I use, and it's remarkably easy. Plug it in, save your stuff, and you're done. I know you say your living situation makes that hard, but I'd trust that before I'd trust some online service. That just raises all kinds of red flags for me.