Perhaps, you've heard that, today, NASDAQ suffered an outage, stoppage, or whatever it is you wanna to call it. No one has an answer right now and could be something harmless (depends on your definition and point of view - maybe not in lost of time and financially) but my first thought was this was an attack or hack.
Here's the scary part. Even now, we don't know. USA Today's post on this matter is a good read.