(CNN) -- Police agencies across Australia put out alerts Monday declaring as fake text messages and emails sent to thousands of Australians that said they had two days to pay $5,000 or die.
"Do not respond," said Detective Superintendent Brian Hay of the Queensland Police Service. "Delete it immediately and don't panic, because that's what they prey upon."
The messages started assaulting mobile phones and email accounts Sunday. Police did not provide an exact figure but said they were surprised by the scope of the scam.
"What is extraordinary in these circumstances is the extent of contact across the Australian landscape," Hay said. "We've never seen this before. I've never seen this before."
While authorities are still investigating, past hoaxes have originated in west Africa, typically Nigeria, he said.
The message reads: "Sum1 paid me to kill you. Get spared, 48hrs to pay $5000. If you inform the police or anybody, death is promised." It then directs the recipient to contact them at a Yahoo email account.
Police say seniors and those not familiar with the Internet are most likely to get scammed.
"They rely upon your fear to not think logically, but to respond in the manner in which they want you to," Hay said. "I would suspect that people have already fallen victim to this fraud."
The so-called hit-man scam has had two previous forays in Australia over the last two and a half years, according to Hay.
"This is not a random event. This is organized crime," Hay said, noting the complexities of pulling off a scam of this magnitude.
"They've done their research. They've acquired their contact lists. They've paid for the distribution of the text messages."
Hays warned that the criminals will be back again if their efforts prove profitable enough.