PORTLAND, Maine (AP) — Drivers may have gotten a chuckle out of an electronic message board in Maine warning of zombies, but city officials were not amused.

The sign at a Portland road construction site was changed by a hacker to read “Warning Zombies Ahead!” on Wednesday morning. It originally read “Night work 8 pm-6 am. Expect delays.”

City spokeswoman Nicole Clegg says the signs are a safety precaution and changing it could have led to driver distraction.

She tells The Portland Press Herald tampering with a safety device is a misdemeanor punishable by up to a year in jail and a $1,000 fine.

She says it’s not clear who changed the sign, but it’s not the first time it has happened.