Hackers tweaked an electronic construction sign along Arapahoe Road in Boulder to read “WARNING DALEKS AHEAD,” referencing a villainous race of extraterrestrial mutants from the long-running British sci-fi TV series “Doctor Who.”

The sign, on eastbound Arapahoe before 48th Street, displayed the mutant warning Tuesday night and into Wednesday morning, but the message was fixed during the day to warn of delays ahead.

Pranksters also struck road signs in Boulder last spring to warn motorists on Foothills Parkway that there were “ZOMBIES AHEAD.”

City of Boulder officials said Wednesday that the sign is maintained by the Colorado Department of Transportation.

CDOT spokeswoman Ashley Mohr said workers were reprogramming the sign midday Wednesday.

“It was locked, so we’re not quite sure how folks were able to break into it,” she said. “But we’re looking into it.”

When the “ZOMBIES AHEAD” sign appeared last year, CDOT workers had accidentally left the message-entry box unlocked.