Authorities have issued an urgent warning for Australians to be on the lookout for savvy scammers who assume the digital identities of loved ones.

It follows a recent surge in dodgy text messages and phone calls that have swindled people out of potentially millions of dollars.

The latest tactic by online criminals has seen people received messages on Facebook from friends or family members asking for cash.

In some cases, victims are told about a competition or easy to obtain government grant that requires a nominal payment for shipping or tax.

“Because the message is from someone you know the scammers hope you’ll trust what they’re telling you,” a Queensland Police spokesman said.

“The message is really from a scammer who has either hacked your friend’s account or created a copy profile by stealing their images and information.”

At comes a week after fresh warnings were issued over a text message purporting to be from Qantas, telling recipients they had won a “mystery box” competition.

Scammers have spoofed the SMS domain of the airline to make the message appear genuine, and it lobs alongside previously sent aboveboard communications from the company.

“You’ve won our mystery box this week,” the message reads. “Please use this link to schedule the delivery.”

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Qantas said it is aware of the scam texts and has urged its customers not to follow the URL.

“These messages are not genuine and encourage customers to click on a link which requests personal information,” the airline said.

“Unfortunately scammers can change sender ID names, which makes it confusing for the recipient to recognise when a legitimate message has been sent and when it is a scam.

“These messages — because of the sender ID name — can then be grouped with genuine messages with Qantas.”

A number of people have also been stung by a telephone scam where criminals claim to be from the Australian Taxation Office and make a number of alarming threats.

In voicemails left by the callers, a robotic-sounding voice warns the recipient that they are the subject of a lawsuit and should return the call immediately.

If they don’t, a warrant will be issued for their arrest, the message threatens.

It’s the latest iteration of a well-worn scam which demands payment of a tax debt — and it has fleeced unsuspecting and terrified victims out of thousands of dollars each.

The ATO has received 28,000 reports about attempted scams since July 1, with the lawsuit-related telephone call among them, and Assistant Commissioner Kath Anderson said fraudsters are growing increasingly sophisticated and hope to exploit vulnerable people.

“Be wary if someone contacts you demanding payment of a tax debt you didn’t know you owed,” Ms Anderson said.

Cyber crime detectives have also identified a spike in the number of threatening emails received by people across the country.

The messages contain terrifying threats designed to frighten people into handing over their money.

The extortion emails demand payment to bitcoin accounts.

The emails have been linked to similar campaigns around the world using sextortion, bomb hoaxes, fake hitman emails and more recently, acid attack threats.

In 2017, Australians lost an estimated $340 million to cyber crime activities — the highest amount on record.