The best advice ever when running random code posted in a forum, is exactly as Stephen alluded to:
NEVER run code that you don't know what it is going to do. Perhaps you wanted to run this script because you saw it as a batch-bomb of sorts, and wanted to look into how to prevent it from crashing your system. But not
knowing?... just don't do it.
For example, DON'T run this:
start "" %0
until you know what it does, and how to stop it. And now that you've seen the code, you'll be able to spot it in the wild.