Hackers could be behind phone threats

Threatening phone calls to schools across Australia could be the work of teenage hackers using online programs to make untraceable calls and create computer-generated voice messages.

They could also be the work of criminals, but authorities remain tight-lipped about their investigations, even as schools across Australia on Wednesday received threatening phone calls for the fourth time in a week.

Schools in Queensland and NSW also received threatening phone calls again on Wednesday.

Victoria Police are investigating whether some may have originated from a selective Melbourne school, but a technology researcher says someone could have falsified the call origin to make it look like it had come from Nossal High School.

Not much is publicly known about the calls other than they are automated, and threatening.

"We don't know who is behind it, or what tools they are using," University of Melbourne hacking researcher Suelette Dreyfus told AAP on Wednesday.

"We don't know anything about them, if they're in Australia or overseas."

It's possible an account on an online phone service may have been hacked and used to make the calls.

A hoax of this nature and scale suggests whoever is behind it has good technology skills, Dr Dreyfus says.

"I'm surprised at how rapid-fire these calls are - to so many different places, and in such a short amount of time - and how it's affecting so many children," she said.

But each time a hoax call is made, the perpetrator risks exposing information about themselves or their location.

"If the hackers or hoaxers have been bad about their operational security, then I think it might be a relatively short time before police are knocking on their doors," Dr Dreyfus said.

"But if they've been very good about it, it could be quite some time."

Since Friday, an undisclosed number of schools in Australia and overseas have received threatening phone calls, which have prompted emergency evacuations.

"The question is, are these guys real criminals, are they teenage hackers who are hoaxing people?," Dr Dreyfus said.

"Either way, they're causing a lot of stress to parents who are probably very worried about the safety of their children."

Last Friday an automated message warned schools a bomb was on their premises, and on Tuesday the threats were either about a bomb, or that shooting would occur.

The principal of Berwick Lodge Primary in Melbourne - which received a threatening phone call on Friday - said if disruption is the aim, it is working.

"We come to work wondering whether the next call is going to be one of these threats," Henry Grossek said.

"We're mentally exhausted."