Contrary to what a construction sign said on state Highway 1 on Sunday and Monday morning, zombies did not wreak havoc in San Francisco last weekend.

The sign was the target of hackers who apparently cracked open a lock on a control box, keyed in a password and typed in “Zombies Plunder SF” in place of what should have been a ramp-closure notice for the Presidio Parkway road project.

Molly Graham, a spokeswoman for the Caltrans project, was not amused.

“It is a crime, and it is vandalism,” Graham said. “It’s important for us to get messages out on highway construction.”

Graham said the sign was changed Monday morning after numerous calls from drivers.

Hacked signs, specifically those having to do with zombies, have been seen nationally. A similar warning in Austin, Texas, cautioned “Zombies Ahead” in 2009, and earlier this year a traffic sign outside a school in a Seattle suburb prompted students to walk toward moving traffic while acting like zombies.

Caltrans spokeswoman Traci Ruth said sign hacking, zombie-related or otherwise, hasn’t been a big problem in the Bay Area, but Graham didn’t want to encourage more zombie messages by revealing the exact hacking method.

Hacker websites have noted in the past that agencies in charge of the signs often don’t modify  the control boxes’ standard passwords, which makes them vulnerable.

In this case, a physical lock was broken before any electronic invasion occurred, Graham said. She said Caltrans currently has no leads or suspects in the incident, but she’s pretty sure the culprit wasn’t affiliated with zombies or the undead of any sort.

“That’s the good news,” she said.

dschreiber@sfexaminer.com