File and Folder ownership settings

[dissect]

I recently re-installed Windows 7. Today I was looking over some of my files and folders, and noticed under "Advanced Security Settings" - "Current Ownership" it no longer lists my name or computer name, but a code "S-1-5-21-#############. It also lists this code if I look under any random image property (properties - details - owner). I've never seen this before after previous re-installs or os's. Can someone tell me what this is or if I've been hacked? I don't want to go through ever single file and folder to change the ownership either.

 

[samuria]

Welcome to the forum the numbers your seeing is the sid windows allocates the sid to every user it's like your name it's often if you have kept old folders the sid would be your old login even if you use the same name the sid is different if it's old it can't display the name hence the sid