Two uni students who had the idea "Would be cool to play a video game on that" when they saw the electronic billboard across the square from their school, actually did hack that billboard to play space invaders last week. The billboard company responded by giving them free iPads.
“This has never happened before, but we appreciate the fact that these guys have, in a charming way, pointed us to this huge problem,” Slobodan Petrovic, the manager of the billboard ad company, DPC said to Kurir-info.rs

Yes, best not leave the electronic billboards that unsecured, they are online after all. Settings these things up, charging a metric crapton™ for the media space and then leaving the billboard totally unsecured seems like a bad case of hubris. Imagine of someone hacks a Coke billboard to Pepsi-fy it. Hang on, I got call TBWA.

Here's the "Vodoo people" video from when Ivan Petrović and Filip Stanisavljević hacked the Billboard last week. Ivan and Filip are white hat hackers and have to spoken to Arstechnica about this, hoping to get employed in computer security in the future. This is actually a pretty good resumé for them too.