Sacramento, Calif. ? Hoover High canceled a student rally Friday because of anonymous text messages that threatened a campus shooting.

Across town, students at Sunnyside High and Ayer Elementary schools went into a 30-minute lockdown Friday for the same reason: someone had threatened students via anonymous text messages.

The threats were the latest in a string this week that caused concern in Valley schools, highlighting what officials say is a growing problem – a high-tech version of pulling the fire alarm.

“It appears to be a new fad,” said Jake Bragonier, spokesman for the Madera Unified School District. He called text messaging this generation’s version of the telephone bomb scare.

Madera Unified has yet to deal with a threatening text messages, but officials think it’s just a matter of time, Bragonier said.

The problem doesn’t just affect schools. Authorities say text messages have been used to scam Fresno residents, spread fear in other cities about gang initiations, and fuel race riots in Australia.

It’s usually done anonymously. The sender generally can remain anonymous by blocking the caller-ID function on his or her cell phone.

“The technology gives them a disguise,” said Eric Hickey, a Fresno State University criminologist and the forensic studies director for San Francisco-based Alliant International University.

Just this week, five high schools in the Valley have had to deal with threatening text messages. Police investigated the incidents, but no one has been arrested.

“It’s frustrating for police, because kids see this stuff on the news and want to copy it,” Reedley Sgt. Todd Lowery said Friday.

And school officials say they have to take all the threats seriously, even if it’s not initially clear whether there’s any substance to them. The proliferation of cell phones doesn’t help, but many parents want their children to have them in case of an emergency on campus.

Text messages, Web postings and phone calls about possible violence caused hundreds of high school students to skip school in the towns of Reedley and Sanger, Calif., earlier this week. The rumors then spread to nearby Orange Cove, Calif., where they caused a commotion at the high school campus but not a lockdown.

“They want the hoopla, the sirens and the chance to get out of class,” Lowery said. “But all they are doing is causing notoriety for their schools.”

Hoover High went into lockdown Thursday after several students received text messages that threatened a lunchtime shooting. Those text messages also caused Hoover officials to cancel Friday’s sports rally, said Fresno Unified School District’s spokeswoman Susan Bedi.

“We are taking the threats seriously,” said Bedi.