Around 50 college campuses across the US have been deluged in recent weeks with hoax calls about armed gunmen and other violence, laying bare the challenges of detecting fake threats quickly to prevent mass panic.

Students at some schools spent hours hiding under desks, only to find out later it was someone's idea of entertainment. On Thursday, several historically Black colleges locked down or cancelled classes after receiving threats, at a time when the fatal shooting of conservative activist Charlie Kirk at a Utah college had campuses on edge.

In other cases, schools figured out early that something was amiss, but even then it took time and resources.

The FBI is investigating, but so far there have been no arrests.

Dispatch call centres often are the last lines of defence, a burden

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