More than three quarters of a million Australians were the victims of identity theft in the past year, costing the average victim about $4,000, credit bureau Veda says.

Illegally obtained personal information fuels cybercrimes like online theft, the company said, and globally, billions of dollars are lost to cybercrime.

When thieves broke into Rhonda's supposedly secure mailbox she thought it was just another ordinary theft.

But five months later she got a text message from her bank asking her to confirm that she had changed her mobile number.

"I received a text basically advising me that if the changed mobile number wasn't correct to contact them immediately," she told the ABC's AM program.

Rhonda immediately went to an ATM to check her account.

"And when I went there it had gone from a $6,000-plus account down to a dollar," she said.

The thieves had obtained her name and date of birth, as well as some basic account details.

Rhonda said it was enough for them to access her account through telephone banking.

"They'd stolen my mail and got a certain amount of information that gave them enough to start getting them through some protocol with the bank," she said.

"Then I believe from there, you know obviously we're all very active on social media, they were able to get further details."

Rhonda was one of 772,000 Australians who have been victims of identity theft in the past 12 months.

How criminals steal your identity

A survey conducted by Veda shows one in five Australians have had their personal information stolen at some point.

Veda's head of cybercrime, Fiona Long, said cybercrime was costly and frustrating for victims.

"At a cost of around $1.6 billion to the economy in the last year, $4000 per incidence and 18 hours to resolve each issue," Ms Long said.

Veda is urging people to make sure they don't share too much personal information on social media.

"The reality is it's happening and it can be stressful and very time consuming experience for Australians."

She said criminals employed a variety of high- and low-tech methods to get hold of personal information.

These include the use spyware or malware, the monitoring of social media and even car and house theft.

"So once the criminals have recreated enough of your identity, they can open accounts, buy a phone for example, they could get a loan, or file a tax return in your name, or even buy a car," Ms Long said.

"There's many things they can do. In fact I spoke to one person recently who had the title deeds of his house transferred to another person, so it can be quite a big impact."

Veda urged people to take simple steps to protect themselves from the growing problem of identity theft.

Ms Long said people could prevent identity theft by using secure mailboxes, shredding personal documents and being extremely careful with the information they share on social media.

Securing personal online information

Rhonda was stung by her experience and is determined never to be a victim again.

She now gets her bank statements and most invoices sent as emails, and she has become extremely careful when using social media.

"I change my password on a regular basis, obviously I don't have my address there," she said.

"I don't put any of my work details or my history of my education and I've even gone so far as to change the date of birth, because you need one to set up a fake Facebook account.

"So I've changed most of that detail."