DALY CITY, Calif. -- Police have arrested a 15-year-old Westmoor High School student in Daly City after the boy threatened to "shoot everyone at school" in an internet message posting this week, authorities said.

According to police, the message, which was posted on www.highschoolnation.com, read, "Note to Self: Shoot everyone at school. On Feb. 7, there will be a terrible murder. Watch your backs, everyone!"

Police received a call from the high school's administration on Tuesday alerting them of the threat.

Detectives were able to trace the message to an internet connection registered to the boy's parents, according to Sgt. Donald Griggs.

Taken to the police station for an interview, the student ultimately admitted to posting the message on the internet, Griggs said.

Officers who searched the family's home reportedly recovered a .22-caliber revolver, several air pistols and a pellet rifle.

The parents reportedly told investigators that they were "stunned" to learn of the incident, police said.

Dick Morosi, principal of Westmoor High, said the boy will face expulsion from the school.

"He was a pretty decent kid who probably didn't understand how serious this was," Morosi said.

The boy was taken to the San Mateo County Juvenile Detention Center on charges of making terrorist threats over the Internet. No court appearance date had been set as of Thursday afternoon.