Students were evacuated from a number of schools across the US after threats were made in what could be the latest example of so-called "swatting" against schools.
In recent months, hoaxers playing online games have allegedly used proxy servers and other high-tech identity-disguising tools to anonymously threaten schools online or in phone messages with electronic voices to trigger a huge police response, including SWAT teams.
Schools in Australia and New Zealand have also been hit by these hoax calls, with 27 schools affected in NZ on one day alone on February 25.
The latest threats in the US led to the evacuation of schools in Colorado, Delaware, Minnesota, New Hampshire and Wisconsin on Monday. Media outlets in the UK also reported evacuations.
The threats were made against primary, middle and high schools, with some schools choosing to continue classes and others to put buildings on lockdown rather than evacuate. Some schools resumed classes after sweeps by authorities failed to turn up explosives or other threats.
Some officials described Monday's threats as automated or robotic and at least two - at Lakewood High School outside Denver and at Ben Franklin Elementary School in Rochester, Minnesota - came in just before noon local time. Also in Minnesota, Forest Lake Elementary in the city of Forest Lake was evacuated after getting a bomb-threat call around 12.15pm.
Two primary schools were evacuated in Colorado - Liberty Point Elementary School in Pueblo West and Cherokee Trail Elementary in the Denver suburb of Parker.
Cherokee Trail is in the same district where two 16-year-old girls are accused of plotting an attack against their high school. No other schools in the district were evacuated, spokeswoman Paula Hans said.
