A man has lost $70,000 to scammers who convinced him tellers at his bank could be trying to hack him.

There has been a "massive" increase in scams in the past couple of weeks, Geeks on Wheels director Cathy Empson said.

"We would expect to get usually about 200 calls a month, which still seems high, but that number has doubled in the last couple of weeks."

Scammers are calling victims to warn them about people trying to hack their bank account. They make them believe they have transferred money into their account, and ask them to transfer the money to another overseas account to help catch the fictional hackers.

In the process the scammers gain access to the victim's computer and capture their bank account password.

"They actually make them believe that the people at the bank could be the ones hacking them," Empson said.

Scammers tell the victim's to "play it cool" at the bank so as to not raise the suspicion of the tellers.

"They really build their trust and they really make it sound like everything you do is going to be really helpful - 'we don't this to happen to other people, we really want your help to catch them'."

A man from Dunedin is one of the most recent victims of the scam. He called Geeks on Wheels on Tuesday to tell them he had lost $70,000.

Another woman from Christchurch also lost $20,000 last Friday.

The money is not recoverable as it is quickly transferred to other bank accounts then put into cash bonds, Empson said.

Some banks have a holding system where for a period of time they do not allow the money to be retransfered, but victims do not usually realise in time that they have been hacked.

This is partly due to the scammers warning them not to log into their bank account, because it could give the "hackers" another chance to steal from them.

The victims from Dunedin and Christchurch were not elderly, but were simply "genuinely nice" people who thought they were helping to catch the hackers.

"It's pretty scary, and to be preying on people who are so willing and wanting to help . . . it's just awful, really."

Scammers would also call people using an area code that matches their city, so as to not raise suspicion.

Empson wanted to warn people not to trust anybody who calls them.

"Nobody will call you to ask you to change your password. Nobody will call you to ask you to load anything on to your computer. The bigger companies don't care if you've been hacked, they're not going to call you to tell you that."

If someone received a call that sounded similar or seemed suspicious in any way, people should ask for the caller's name and department, then independently look for the number of the company and call back to see if the call was legitimate.

Anyone uncertain about what was going on could call 0800 4 A GEEK (0800 424 335) for free expert advice.