Pranksters in at least three US states have figured out how to alter the text on electronic road signs, posting notices of "Nazi zombies" and "raptors ahead" instead of legitimate messages detailing traffic problems.

The latest breach came on Tuesday during the morning rush hour near Collinsville, Illinois, where hackers changed a sign along southbound Interstate 255 to read, "DAILY LANE CLOSURES DUE TO ZOMBIES."

A day earlier in Indiana's Hamilton County, the electronic message on a board in Carmel's construction zone warned drivers of "RAPTORS AHEAD."

Signs in Austin, Texas, recently flashed: "NAZI ZOMBIES! RUN!!!" and "ZOMBIES IN AREA! RUN."

"We understood it was a hoax, but at the same time those boards are there for a reason," said Joe Gasaway, an Illinois Department of Transportation supervisory field engineer. "We don't want (drivers) being distracted by a funny sign."