A former ASB banker who stole $18 million from customers and blew $3.4 million of it on prostitutes has been sentenced to six years in jail.

Stephen Gerard Versalko, 52, married with three children, lived the high life for nine years after scalping $17,763,110 off 26 wealthy ASB clients.

SFO prosecutor Patrick McCann said Versalko had paid $3.4m to two female Auckland prostitutes over the course of the nine years.

Versalko's lawyer Stuart Grieve QC claimed at least part of that was extorted from Versalko by one of the women who tried to blackmail the banker - though the SFO says it knows nothing about any blackmail.

He preyed on elderly women who lived overseas and were unsophisticated about money, SFO prosecutor Patrick McCann told the court.

Versalko, wearing a short sleeved top and pin stripe pants, was sentenced to six years jail by judge Chris Field in the Auckland District Court, eligible for parole after four years.

The judge said it would have been higher, except Versalko admitted the crimes early and helped the SFO unpick his web of money transactions and enable the recovery of $4m.

Amongst other perks he bought himself from the fraud was a $3.2 million home in plush Remuera.

He also scored himself a $1.8 million beach front holiday home at Whangapoua in the Coromandel.

A senior investment adviser, he was finally caught out when one of the ASB clients saw a documentary on jailed US fraudster Bernie Madoff and became suspicious of Versalko.

She realised Versalko was the only person from the ASB she had any contact with about her investments - which promised higher than normal interest, no tax and no fees.

She rang the bank, which soon uncovered the fraud. He was fired in August last year.

The Serious Fraud Office laid three charges just before Christmas and he pleaded guilty earlier this year.

His lawyer Stuart Grieve, QC, said Versalko had shown "exceptional remorse" and deserved credit for admitting the fraud and helping the SFO track down where all the money went.

For the first time the details of the case, which have been suppressed, were made public.

Mr McCann said Versalko was running a "classic ponzi scheme" - where he promised clients interest and repayments, then stole from new investors to make those repayments, all the while siphoning off money for his life style.

The ASB Bank has already reimbursed all the clients ripped off by Versalko and were in the process of recovering money from Versalko.

ASB takes any matters of fraud very seriously and is pleased that the SFO investigation has culminated in Stephen Versalko being sentenced to imprisonment after pleading guilty to his criminal activity.

In a statement ASB said only a very small number of customers were affected by Versalko’s offending and all had been reimbursed and apologised again to customers affected.

ASB said as a result of the fraud it had introduced additional processes and practices to further strengthen security and protect customers.

Versalko's fraud contributed to driving the ASB Bank to its first loss in 20 years in its accounts for the first half of the current financial year.