Does anyone here knows anything about System Volume Information?

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Last November I had this issue with my external drive, one evening I was shocked to find out that all my files in my external drive are gone. And all I can see was an icon or a thumbnail labeled as System Volume Information. When I researched for it in the internet, as far as I could understand it's a folder created by Windows, in this case it's Window 7. But you can't access it like a regular folder, unless you make some changes on your computer's security settings by going to your Folder Options, then to View, and uncheck "Show hidden files and folders" and "Hide protected operating system files". That way I was able to retrieved all my files from that System Volume Information folder and save it all temporarily to my laptop's My Document folder. And then I reformatted my external drive and I saved all my files back to my external. But unfortunately in the process of doing all that, it made my laptop's speed to slowdown tremendously even after I have deleted all the copies of the files from My Document folder. I think I should reformat everything in my laptop as well. Anyway, my conclusion is, my external drive may have been infected with virus and Window 7 created the System Volume Information folder to protect my files. So can anyone tell me if my conclusion is correct or is there anyone can tell me in layman's term what is the real purpose of System Volume Information?