New Zealand's largest credit bureau says more than 200,000 people are using false information to scam the system.
Veda has a database of about 3.2 million files with information on every credit-active New Zealander over the age of 18.
Managing director John Roberts said 216,000 people had an alias name and adverse information on their file, and that number is on the rise.
"In the last 12 months it has grown by 10 percent. You tend to find that it's quite a large base that keep on trying to you know, game the system.
"In fact, one particular person on the bureau has actually got 27 different aliases recorded. So this is a constant problem," he said.
Mr Roberts said tens of millions of dollars were written off each year because of fraud, and the best defence was to check people's credit history and ensure they had proof of their identity.