Police across Australia warned mobile phone users on Monday to ignore a text message sent to "a large number of people" threatening death if they did not pay Aus$5,000 (US$5,150).
"Sum1 paid me to kill you. get spared, 48hrs to pay $5000. If you inform the police or anybody, death is promised...E-mail me now: firstname.lastname@example.org," read the text.
It prompted hundreds of calls to authorities from worried recipients.
Police in the states of New South Wales, Western Australia, Victoria, Queensland, South Australia and Tasmania all issued statements telling recipients not to be alarmed.
Queensland police said the hoax was commonly referred to as "the hitman scam".
"If any member of the public has transferred any money it is vital they contact police and their bank immediately," they said.
New South Wales police said there had been a "major" increase in emergency calls.
"The origin of the message is under investigation. However, police do not believe it poses a genuine threat," they said.
Most scams originate overseas, making them difficult to track down and prosecute, said the Australian Competition and Consumer Commission, which runs a "scamwatch" website.
Explore further: Japan court orders Facebook to reveal revenge porn IP addresses