A fake Amber Alert for a 7-year-old girl is spreading like wildfire through text messages, Twitter and the Internet, causing concern for authorities.

"AMBER ALERT! A 7yr old girl was taken by a man driving a newer silver truck. The license plate reads 72b381, please forward!" it says.

Depending on which version of the text-message alert you receive, it's either a truck or a car and from Idaho or Arizona. The alert, which has taken on a life of its own within the past 24 hours, has authorities concerned about someone using the Amber Alert to cry wolf.

"It's being spread around by people who want to help," said Paul Murphy, the Utah attorney general's Amber Alert coordinator. "They are preying on people's good intentions."

Murphy said he first heard about it when contacted Sunday night by KSL, which had viewers claiming there was an Amber Alert when he had not issued one. The station emits the emergency alert system, which is how an Amber Alert is put out to TV and radio stations statewide.

The National Center for Missing and Exploited Children said it has found no such child or even such a case. The U.S. Justice Department said NCMEC is unaware of any active Amber Alerts at this time and it appears to be a hoax.

Utah did not activate its Amber Alert, which sends out an alert to broadcast stations, freeway signs, Web sites and cell phones. However, the hoax appears to be spreading by itself thanks to forwarded text messages and the Twitter micro-blogging service.

This isn't the first time a phony missing child report has given authorities anxiety. The Utah Attorney General's Office grappled with one last year that began with a text message saying: "AMBER ALERT! two little girls kidnapped the suspect is driving a brown jeep liberty. Headed towards billings area license plate #43-6519. KEEP THIS GOING!"

Two girls had not been kidnapped, no one had issued an Amber Alert and there wasn't enough information that would typically be included in such an alert. A real alert in that case was issued in Montana in April 2008 and the girls had already been recovered by the time the text message hit cell phones in Utah.

There are several famous viral e-mails about abducted children that have duped millions. "Penny Brown" is missing in a hoax e-mail that's been circulating since 2001. Ashley Flores, 13, has been missing for two weeks since 2006. The NCMEC said it has never found a missing child by her name or description, but the e-mail includes a photo of a smiling teenage girl.

While it's hard to tell where these fake Amber Alerts come from, if it originated in Utah the prankster could face a class B misdemeanor charge of making a false report. Murphy said the fake reports cause real anxiety for law enforcement.

"It's frequent enough to cause concern and when a real Amber Alert goes out we want people to be aware and do what they can to help find a child," he said. "We don't want them to have anxiety when a fake alert goes out."

E-mail: bwinslow@desnews.com