(Harrisburg) -- Electronic road signs can be pretty easy to hack, and across the country, message boards have warned of impending doom from raptors and zombies, instead of slick roads.

PennDOT says it has a two-step system in place to keep pranksters at bay.

An agency spokeswoman says access to roadside signs, as well as highway advisory radios is protected with an employee-specific password and a physical locking system.

Chuck Davis, who teaches ethical hacking and computer forensics at Harrisburg University, says that's probably adequate.

"It's very simple to change the sign unless there's a padlock on the back," he says. "So I would say that from a protection standpoint, putting the password on here is a good idea, but since that can be circumvented, also putting a padlock and otherwise physically securing the keyboard is probably the best mode of protection.

An electronic roadside sign in San Francisco intended to warn drivers about street delays was recently hacked to read, "TURN BACK," and "GODZILLA ATTACK."

"Turns out that quote unquote hacking this is rather simple," Davis says.

Five years ago, a website published step-by-step instructions for hacking electronic signs, highlighting security shortcomings.