A Caltrans spokesperson said someone had apparently reprogrammed the northbound 15 Freeway sign at Ontario Avenue to read: "Inland Empire supports Donald Trump. Merry Xmas. Vote Donald Trump."
As opposed to its usual traffic warning, the sign with the Trump message was clearly visible to thousands of passing motorists for an unknown period of time.
The Riverside County Transportation Commission said the sign was a prank.
"Someone accessed the message sign. Hacked into the message and changed it for their own purposes," said Anne Mayer with the commission.
Officials said enhanced security measures will be enforced. However, when Eyewitness News headed out to the sign that was tampered with, the program box was unlocked.
Meyer said despite the box being unlocked, there is a passcode that needs to be entered in order to access the sign's program. She said someone may have hacked into the program in order to figure out the passcode.
Nikki and Dann Worden, of Corona, were returning home from the movies when they said they couldn't believe what they saw. So, they decided to get off the freeway and pass it again while recording it on video.
After Worden posted the video on Facebook, the post received over 260,000 hits from people viewing and sharing her video.
By Saturday morning, the display was back to its original traffic message.