Those circular keys aren't any kind of security at all. The only difference in them is generally the diameter of the circle. My old roommate in college used to collect those on a key ring for fun and pranks. When we moved into the dorm, he noticed that my Gateway 2000 desktop computer (circa 1995) had one of those round keyholes on the front of it. I guess for corporate or industrial use or something, it's an input lockout, so locking that round keyhole cuts off the mouse and keyboard input. So I get back from class one day, and my keyboard and mouse won't work, and he's snickering because he saw the lock and as a prank, found one of the keys on his ring that fit it and locked it.
He also did the old prank of screen shotting my desktop, setting that as my background picture and removing the icons, so it looks like normal, but double clicking the program icons doesn't do anything because it's just an image of them.